Zirconia-toughened glass ceramics

ABSTRACT

ZrO2-toughened glass ceramics having high molar fractions of tetragonal ZrO2 and fracture toughness value of greater than 1.8 MPa·m1/2. The glass ceramic may also include also contain other secondary phases, including lithium silicates, that may be beneficial for toughening or for strengthening through an ion exchange process. Additional second phases may also decrease the coefficient of thermal expansion of the glass ceramic. A method of making such glass ceramics is also provided.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.17/188,635 filed on Mar. 1, 2021, which claims the benefit of priorityunder U.S. patent application Ser. No. 16/310,133 filed on Dec. 14,2018, which claims the benefit of priority under 35 U.S.C. § 371 ofInternational Application No. PCT/US2017/039233, filed on Jun. 26, 2017,which claims the benefit of priority under 35 U.S.C. § 119 of U.S.Provisional Application Ser. No. 62/512,418 filed on May 30, 2017,62/361,210 filed on Jul. 12, 2016, and 62/354,271 filed on Jun. 24,2016, the content of each is relied upon and incorporated herein byreference in their entirety.

FIELD OF DISCLOSURE

The disclosure relates to glasses and glass ceramics. More particularly,the disclosure relates to glass ceramic-containing tetragonal zirconiasalong with the glasses that form these glass ceramics. Even moreparticularly, the disclosure relates to glass ceramic-containingtetragonal zirconias having high fracture toughness.

BACKGROUND

Transformation-toughened ZrO₂ ceramics are among the toughest andstrongest of the engineering ceramics, and are typically produced viaceramic processing techniques such as hot pressing or sintering. Inanother approach, prefabricated ZrO₂ particles are dispersed in a matrixof either ceramic or glass. In this case, the ZrO₂ fraction of the finalproduct is substantially lower than that of the pure ceramic material.Generally, these ceramics are generally monolithic-stabilized oxides,such as Ca, Mg, Ce or yttria-stabilized ZrO₂, where the principle phaseof the monolith is ZrO₂.

In order to realize transformation toughening, it is necessary to obtainthe tetragonal form of ZrO₂ in the as-made part. The tetragonal ZrO₂phase transforms to the monoclinic phase under mechanical stress, whichleads to toughening. However, ZrO₂ undergoes a thermal transition fromtetragonal to monoclinic symmetry or structure at about 950° C. This canoccur during processing of the materials, producing a materialcomprising the “transformed” monoclinic form. Presence of the monoclinicform in the as-made material does not offer the opportunity forsubsequent transformation toughening.

SUMMARY

The present disclosure provides ZrO₂-toughened glass ceramics havinghigh molar fractions of tetragonal ZrO₂ and a fracture toughness ofgreater than 2 MPa·m^(1/2). The glass ceramic may also include othersecondary phases that may be beneficial for toughening or forstrengthening. In some embodiments, strengthening may be achievedthrough an ion exchange process. Additional phases may also impart otherproperties or performance in the glass ceramic, such as decrease thecoefficient of thermal expansion of the glass ceramic. A method ofmaking such glass ceramics is also provided.

In an aspect (1), the disclosure provides a glass ceramic comprising atleast two crystalline phases, the first crystalline phase comprising aZrO₂ phase and the second crystalline phase comprising a lithiumsilicate phase, the glass ceramic further comprising a residual glassphase, whereby the resulting glass ceramic has an improved fracturetoughness of from 1.8 to 10 MPa·min as measured by a chevron notch shortbar method.

In another aspect (2), the disclosure provides the glass ceramic ofaspect (1), wherein the first crystalline phase is a tetragonal ZrO₂phase. In an aspect (3), the disclosure provides the glass ceramic ofaspect (1) or (2), wherein the second crystalline phase is a lithiumdisilicate phase. In an aspect (4), the disclosure provides the glassceramic of any of aspects (1)-(3), comprising the composition: 50-80 mol% SiO₂; 18-40 mol % Li₂O; 1.5-25 mol % ZrO₂, and greater than 0-5 mol %P₂O₅.

In an aspect (5), the disclosure provides the glass ceramic of any ofaspects (1)-(4), wherein the at least two crystalline phases comprise aweight percent (wt %) of the total glass ceramic, measured as the(((weight of the at least two crystalline phases)/(total weight of theglass ceramic))*100), and wherein the at least two crystalline phasescomprise from 30-98 wt % of the total glass ceramic. In an aspect (6),the disclosure provides the glass ceramic of any of aspects (1)-(5),wherein the at least two crystalline phases comprise from 60-95 wt % ofthe total glass ceramic. In an aspect (7), the disclosure provides theglass ceramic of any of aspects (1)-(6), wherein the tetragonal ZrO₂comprises a weight percent (wt %) of the total ZrO₂ in the glassceramic, measured as the (((weight of the tetragonal ZrO₂)/(total weightof ZrO₂ in the glass ceramic))*100), and wherein the tetragonal ZrO₂comprises 40-95 wt % of ZrO₂ in the glass ceramic. In an aspect (8), thedisclosure provides the glass ceramic of any of aspects (1)-(7), whereinthe tetragonal ZrO₂ comprises a weight percent (wt %) of the total glassceramic, measured as the (((weight of the tetragonal ZrO₂)/(total weightof the glass ceramic))*100), and wherein the tetragonal ZrO₂ phasecomprises 5-25 wt % of the total glass ceramic. In an aspect (9), thedisclosure provides the glass ceramic of any of aspects (1)-(8), whereinthe tetragonal ZrO₂ comprises a weight percent (wt %) of the totalcrystalline phases of the glass ceramic, measured as the (((weight ofthe tetragonal ZrO₂)/(total weight of the crystalline phases of theglass ceramic))*100), and wherein tetragonal ZrO₂ phase may comprise5-50 wt % of the total crystalline phases of the glass ceramic.

In an aspect (10), the disclosure provides the glass ceramic of any ofaspects (1)-(9), wherein the tetragonal ZrO₂ crystals have an averagecrystal size from 0.1 to 10 μm along their longest dimension. In anaspect (11), the disclosure provides the glass ceramic of aspect (10),wherein the tetragonal ZrO₂ crystals have an average crystal size from0.3 to 7 μm along their longest dimension. In an aspect (12), thedisclosure provides the glass ceramic of aspect (11), wherein thetetragonal ZrO₂ crystals have an average crystal size from 0.5 to 4 μmalong their longest dimension.

In an aspect (13), the disclosure provides the glass ceramic of any ofaspects (1)-(12), wherein the lithium disilicate comprises a weightpercent (wt %) of the total glass ceramic, measured as the (((weight ofthe lithium disilicate)/(total weight the glass ceramic))*100), andwherein the lithium disilicate comprises from 25-60 wt % of the totalglass ceramic composition. In an aspect (14), the disclosure providesthe glass ceramic of any of aspects (1)-(13), wherein the lithiumdisilicate comprises a weight percent (wt %) of the total crystallinephases of the glass ceramic, measured as the (((weight of the lithiumdisilicate)/(total weight of the crystalline phases of the glassceramic))*100), and wherein lithium disilicate phase may comprise 5-50wt % of the total crystalline phases of the glass ceramic. In an aspect(15), the disclosure provides the glass ceramic of any of aspects (1)(14), wherein the lithium disilicate crystals have an average crystalsize from 1 to 20 μm along their longest dimension. In an aspect (16),the disclosure provides the glass ceramic of aspect (15), wherein thelithium disilicate crystals have an average crystal size from 5 to 15 μmalong their longest dimension.

In an aspect (17), the disclosure provides the glass ceramic of any ofaspects (1) (16), further comprising one or more additional crystallinephases. In an aspect (18), the disclosure provides the glass ceramic ofaspect (17), wherein the one or more additional crystalline phases isselected from the group consisting of lithium aluminosilicate,cristobalite, beta-spodumene, lithiophosphate (Li₃PO₄), lithiumorthophosphate, quartz solid solution, baddeleyite, lithium metasilicate(Li₂SiO₃), monoclinic zirconia, cubic zirconia, or (Na,Li)ZrSi₆O₁₈ orcombinations thereof. In an aspect (19), the disclosure provides theglass ceramic of aspect (18), wherein the one or more additionalcrystalline phases is selected from the group consisting of monoclinicZrO₂, lithium aluminosilicate, β-spodumene solid solution, β-quartzsolid solution, or α-quartz or combinations thereof. In an aspect (20),the disclosure provides the glass ceramic of aspect (19), wherein theone or more additional crystalline phases is two or more phases selectedfrom the group consisting of a monoclinic ZrO₂ and at least one oflithium aluminosilicate, β-spodumene solid solution, β-quartz solidsolution, or α-quartz, wherein the monoclinic ZrO₂ is from >0-5 wt % ofthe glass ceramic.

In an aspect (21), the disclosure provides the glass ceramic of any ofaspects (1) (20), further comprising: 0-5 mol % Al₂O₃ and 0-5 mol %Na₂O. In an aspect (22), the disclosure provides the glass ceramic ofany of aspects (1)-(21), further comprising: 0-14 mol % R₂O; 0-10 mol %MO; 0-5 mol % TMO; and 0-5 mol % REO. In an aspect (23), the disclosureprovides the glass ceramic of any of aspects (1)-(22), comprising: 55-70mol % SiO₂; 18-30 mol % Li₂O; 4-20 mol % ZrO₂; and 0.2-5 mol % P₂O₅. Inan aspect (24), the disclosure provides the glass ceramic of any ofaspects (1)-(23) comprising: 58-69 mol % SiO₂; 25-36 mol % Li₂O; 6-15mol % ZrO₂; >0-5 mol % Al₂O₃; 0-5 mol % B₂O₃; 0.2-3 mol % P₂O₅; 0-8 mol% MO; 0-5 mol % TMO; and 0-5 mol % REO. In an aspect (25), thedisclosure provides the glass ceramic of any of aspects (1)-(24) furthercomprising >0-5 mol % REO. In an aspect (26), the disclosure providesthe glass ceramic of aspect (25), wherein REO comprises Y₂O₃ and Y₂O₃(mol %)/ZO₂ (mol %)<0.2. In an aspect (27), the disclosure provides theglass ceramic of any of aspects (1)-(26), wherein the glass ceramic isfree of Rb₂O and Cs₂O. In an aspect (28), the disclosure provides theglass ceramic of any of aspects (1)-(27), further comprising >0-5 mol %TiO₂. In an aspect (29), the disclosure provides the glass ceramic ofany of aspects (1)-(28), further comprising >0-3 mol % ZnO.

In an aspect (30), the disclosure provides the glass ceramic of any ofaspects (1) (29), further comprising >0-4 mol % of a color component. Inan aspect (31), the disclosure provides the glass ceramic of aspect(30), wherein the color component comprises Fe₂O₃, V₂O₅, Cr₂O₃, MnO₂,NiO, CuO, Co₃O₄ and combinations thereof. In an aspect (32), thedisclosure provides the glass ceramic of any of aspects (1)-(31),wherein the glass ceramic exhibit a color presented in CIELAB colorspace coordinates: a*=from about −1 to about +3; b*=from about −7 toabout +3; and L*>85. In an aspect (33), the disclosure provides theglass ceramic of any of aspects (1)-(32), wherein a*=from about −1 toabout 0; b*=from about −2 to about 0; and L*>88. In an aspect (34), thedisclosure provides the glass ceramic of any of aspects (1)-(31),wherein the glass ceramic exhibit a color presented in CIELAB colorspace coordinates: a*=from about −1 to about 1; b*=from about −4 toabout 1; and L*<60. In an aspect (35), the disclosure provides the glassceramic of aspect (34), wherein a*=from about −1 to about 1; b*=fromabout −1 to about 1; and L*<40. In an aspect (36), the disclosureprovides the glass ceramic of any of aspects (1)-(35), wherein the glassceramic has a fracture toughness of from 2 to 10 MPa·m^(1/2) as measuredby Chevron notch short bar methods. In an aspect (37), the disclosureprovides the glass ceramic of any of aspects (1) (36), wherein the glassceramic further comprises an ion exchanged layer, the ion exchangedlayer having a depth of compression of at least 10 μm. In an aspect(38), the disclosure provides the glass ceramic of aspect (37), whereinthe ion exchanged layer has a depth of compression of at least 30 μm. Inan aspect (39), the disclosure provides the glass ceramic of aspect (37)or (38), wherein the surface compression of the glass ceramic is from350 MPa to 800 MPa.

In an aspect (40), the disclosure provides an article comprising theglass ceramic of any of aspects (1)-(39). In an aspect (41), thedisclosure provides the article of aspect (40), wherein the articlecomprises a portion of a housing for a consumer electronic device, theconsumer electronic device comprising the housing and electricalcomponents provided at least partially internal to the housing. In anaspect (42), the disclosure provides the article of aspect (40), whereinthe glass ceramic forms at least a portion of a dental composite, adental restorative, or a dental article. In an aspect (43), thedisclosure provides the article of aspect (42), wherein the dentalarticle is one of a filling, a bridge, a splint, a crown, a partial acrown, a denture, a tooth, a jacket, an inlay, an onlay, a facing, aveneer, a facet, an implant, a cylinder, an abutment, or a connector.

In an aspect (44), the disclosure provides a method of making the glassceramic of any of aspects (1)-(39), the method comprising the steps of:a. providing a precursor glass material, the precursor materialcomprising SiO₂, Li₂O, ZrO₂ and P₂O₅; b. ceramming the precursormaterial to form the glass ceramic, wherein ceramming comprises heatingthe precursor material at a first temperature for a first time period offrom about 15 minutes to about 3 hours, followed by heating to a secondtemperature for a second time period of from about 0.5 hour to 5 hours,wherein the first temperature is in a range from about 600° C. to about850° C. and the second temperature is in a range from about 725° C. toabout 1000° C.

In an aspect (45), the disclosure provides a method of making the glassceramic of aspect (44), wherein the precursor glass material comprises:50-80 mol % SiO₂; 18-40 mol % Li₂O; 3-25 mol % ZrO₂; and greater than0-5 mol % P₂O₅. In an aspect (46), the disclosure provides a method ofmaking the glass ceramic of aspect (45), wherein the precursor materialfurther comprises: 0-5 mol % Al₂O₃ and 0-5 mol % Na₂O. In an aspect(47), the disclosure provides a method of making the glass ceramic ofaspect (45) or (46), wherein the precursor material further comprises:0-14 mol % R₂O; 0-10 mol % MO; 0-5 mol % TMO; and 0-5 mol % REO. In anaspect (48), the disclosure provides a method of making the glassceramic of any of aspects (44)-(47), wherein the precursor materialcomprises: 55-70 mol % SiO₂; 18-30 mol % Li₂O; 4-20 mol % ZrO₂; and0.2-5 mol % P₂O₅. In an aspect (49), the disclosure provides a method ofmaking the glass ceramic of any of aspects (44)-(48), wherein theprecursor material comprises: 58-69 mol % SiO₂; 25-36 mol % Li₂O; 6-15mol % ZrO₂; >0-5 mol % Al₂O₃; 0-5 mol % B₂O₃; 0.2-3 mol % P₂O₅; 0-8 mol% MO; 0-5 mol % TMO; and 0-5 mol % REO.

In an aspect (50), the disclosure provides a method of making the glassceramic of any of aspects (44)-(49), wherein the precursor materialfurther comprises >0-5 mol % REO. In an aspect (51), the disclosureprovides a method of making the glass ceramic of aspect (50), whereinREO comprises Y₂O₃ or CeO₂. In an aspect (52), the disclosure provides amethod of making the glass ceramic of any of aspects (44)-(51), whereinthe precursor material is free of Rb₂O and Cs₂O. In an aspect (53), thedisclosure provides a method of making the glass ceramic of any ofaspects (44)-(52), wherein the precursor material further comprises >0-5mol % TiO₂. In an aspect (54), the disclosure provides a method ofmaking the glass ceramic of any of aspects (44)-(53), wherein theprecursor material further comprises >0-3 mol % ZnO. In an aspect (55),the disclosure provides a method of making the glass ceramic of any ofaspects (44)-(54), wherein the precursor material further comprises >0-4mol % of a color component. In an aspect (56), the disclosure provides amethod of making the glass ceramic of any of aspects (44)-(55), whereinthe color component comprises Fe₂O₃, V₂O₅, Cr₂O₃, MnO₂, NiO, CuO, NiO,Co₃O₄ and combinations thereof.

In an aspect (57), the disclosure provides a method of making the glassceramic of any of aspects (44)-(56), wherein the first time period isfrom about 15 minutes to about 1 hour. In an aspect (58), the disclosureprovides a method of making the glass ceramic of any of aspects(44)-(57), wherein the second time period is from about 0.5 hour toabout 2 hours. In an aspect (59), the disclosure provides a method ofmaking the glass ceramic of any of aspects (44)-(58), wherein theprecursor material comprises a precursor glass. In an aspect (60), thedisclosure provides a method of making the glass ceramic of any ofaspects (44) (59), wherein the precursor material further includesgrinding the precursor glass to a precursor glass powder. In an aspect(61), the disclosure provides a method of making the glass ceramic ofany of aspects (44)-(60), further comprising the step of sintering andceramming the precursor glass powder. In an aspect (62), the disclosureprovides a method of making the glass ceramic of any of aspects(44)-(61), further comprising sintering the glass ceramic. In an aspect(63), the disclosure provides a method of making the glass ceramic ofany of aspects (44)-(62), further comprising hot pressing the glassceramic. In an aspect (64), the disclosure provides a method of makingthe glass ceramic of any of aspects (44)-(63), further comprisingmachining or shaping the glass precursor material prior to heating theprecursor material at the first temperature. In an aspect (65), thedisclosure provides a method of making the glass ceramic of any ofaspects (44)-(64), further comprising machining or shaping the glassprecursor material following heating the precursor material at the firsttemperature and prior to heating the precursor material at the secondtemperature.

In an aspect (66), the disclosure provides the glass ceramic of any ofaspects (1) (43) producible by the process: a. providing a precursormaterial, the precursor material comprising SiO₂, L₂O, ZrO₂, and P₂O₅;b. ceramming the precursor material to form the glass ceramic, whereinceramming comprises heating the precursor material at a firsttemperature for a first time period of from about 15 minutes to about 3hours, followed by heating to a second temperature for a second timeperiod of from about 0.5 hour to 5 hours, wherein the first temperatureis in a range from about 600° C. to about 850° C. and the secondtemperature is in a range from about 725° C. to about 1000° C.

In an aspect (67), the disclosure provides the glass ceramic of aspect(66), wherein the precursor glass material comprises: 50-80 mol % SiO₂;18-40 mol % Liza; 3-25 mol % ZrO₂; and greater than 0-5 mol % P₂O₅.

These and other aspects, advantages, and salient features will becomeapparent from the following detailed description, the accompanyingdrawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings in general, it will be understood that theillustrations are for the purpose of describing particular embodimentsand are not intended to limit the disclosure or appended claims thereto.The drawings are not necessarily to scale, and certain features andcertain views of the drawings may be shown exaggerated in scale or inschematic in the interest of clarity and conciseness.

FIG. 1A is a scanning electron microscopy (SEM) image of a glass ceramicmaterial that was cerammed by heating at 750° C. for 2 hours and thenheating at 900° C. for 4 hours;

FIG. 1B is a SEM image of a glass ceramic material that was cerammed byheating at 800° C. for 2 hours and then heating at 900° C. for 4 hours;

FIGS. 2A-D are SEM images showing the indents after a Vickersindentation at 50 kgf of Example 8. The example composition was cerammedat 750° C. for 2 hours, then 875° C. for 4 hours. The tortuous crackpath and crack deflection by the lithium disilicate and tetragonalzirconia are visible in example;

FIGS. 3A-3D are an SEM image of embodiment Example 8 (FIG. 3A), alongwith SEM elemental mapping of some of the constituents of Example 8,where FIG. 3B shows the silicon present in the material, FIG. 3C showsthe zirconia, and FIG. 3D shows the phosphorous.

FIGS. 4A-4D are X-ray diffraction spectra showing phase assemblages ofembodied glass-ceramics. The figures show that lithium disilicate (LS2)and tetragonal ZrO2 (t-ZrO2) are present in the various embodimentsalong with a number of other phases (lithium metasilicate (LMS),monoclinic ZrO₂ (m-ZrO2)). FIG. 4A shows the phase assemblage forExample 8, FIG. 4B for Example 14, FIG. 4C for Example 40, and FIG. 4Dfor Example 44. All examples were cerammed at 750° C. for 2 hours, then875° C. for 4 hours, except Example 44 which was cerammed at 750° C. for2 hours, then 850° C. for 4 hours.

FIG. 5 is a plot of abraded ring-on-ring (ARoR) data obtained for 0.8mm-thick samples of a non-ion exchanged and ion-exchanged ZrO₂-toughenedglass ceramic (Example 8), which ion exchanged for a number of differenttimes and temperatures.

FIGS. 6A and 6B are comparisons of drop performance for exampleembodiments (Example 14) and ZrO₂ ceramics. All parts are 0.8 mm thick,dropped on 180 grit sandpaper and then survivors on 30 grit sand paper.Example 14 was cerammed at 750° C. for 2 hours, then 875° C. for 4hours; Comp 1 is a reference transparent glass-ceramic; CoorsTek TTZ isa MgO-stablized ZrO₂ ceramic.

FIG. 7 shows the loss tangent of Example 8 versus a reference glass andreference glass ceramic. The example composition was cerammed at 750° C.for 2 hours, then 875° C. for 4 hours.

FIG. 8 shows the dielectric constant of Example 8 versus a referenceglass and reference glass ceramic. The example composition was cerammedat 750° C. for 2 hours, then 875° C. for 4 hours.

FIGS. 9A-9C are micrographs of scratch tests done using a Knoop tip at14 N and 16 N loads for Example 8. The example composition was cerammedat 750° C. for 2 hours, then 875° C. for 4 hours.

DETAILED DESCRIPTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views shown in thefigures. It is also understood that, unless otherwise specified, termssuch as “top,” “bottom,” “outward,” “inward,” and the like are words ofconvenience and are not to be construed as limiting terms. In addition,whenever a group is described as comprising at least one of a group ofelements and combinations thereof, it is understood that the group maycomprise, consist essentially of, or consist of any number of thoseelements recited, either individually or in combination with each other.Similarly, whenever a group is described as consisting of at least oneof a group of elements or combinations thereof, it is understood thatthe group may consist of any number of those elements recited, eitherindividually or in combination with each other. Unless otherwisespecified, a range of values, when recited, includes both the upper andlower limits of the range as well as any ranges therebetween. As usedherein, the indefinite articles “a,” “an,” and the correspondingdefinite article “the” mean “at least one” or “one or more,” unlessotherwise specified. It also is understood that the various featuresdisclosed in the specification and the drawings can be used in any andall combinations.

Where a range of numerical values is recited herein, comprising upperand lower values, unless otherwise stated in specific circumstances, therange is intended to include the endpoints thereof, and all integers andfractions within the range. It is not intended that the scope of theclaims be limited to the specific values recited when defining a range.Further, when an amount, concentration, or other value or parameter isgiven as a range, one or more preferred ranges or a list of upperpreferable values and lower preferable values, this is to be understoodas specifically disclosing all ranges formed from any pair of any upperrange limit or preferred value and any lower range limit or preferredvalue, regardless of whether such pairs are separately disclosed.Finally, when the term “about” is used in describing a value or anend-point of a range, the disclosure should be understood to include thespecific value or end-point referred to. When a numerical value orend-point of a range does not recite “about,” the numerical value orend-point of a range is intended to include two embodiments: onemodified by “about,” and one not modified by “about.”

As used herein, the term “about” means that amounts, sizes,formulations, parameters, and other quantities and characteristics arenot and need not be exact, but may be approximate and/or larger orsmaller, as desired, reflecting tolerances, conversion factors, roundingoff, measurement error and the like, and other factors known to those ofskill in the art. It is noted that the terms “substantially” may beutilized herein to represent the inherent degree of uncertainty that maybe attributed to any quantitative comparison, value, measurement, orother representation. These terms are also utilized herein to representthe degree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue. Thus, a glass that is “free of Al₂O₃” is one inwhich Al₂O₃ is not actively added or batched into the glass, but may bepresent in very small amounts as a contaminant (e.g., 500, 400, 300,200, or 100 parts per million (ppm) or less or).

Unless otherwise specified, all compositions are expressed in terms ofmole percent (mol %). Compositional ranges of crystalline materials inthe glass ceramic are expressed in terms of weight percent (wt %) unlessotherwise specified. Coefficients of thermal expansion (CTE) areexpressed in terms of 10⁻⁷/° C. and represent a value measured over atemperature range from 20° C. to 300° C., unless otherwise specified.The density in terms of grams/cm³ was measured via the Archimedes method(ASTM C693).

Vickers crack initiation thresholds described herein are determined byapplying and then removing an indentation load to the glass surface at arate of 0.2 mm/min. The indenter uses a standard 136° tip angle on adiamond indenter. The maximum indentation load is held for 10 seconds.The indentation cracking threshold is defined at the indentation load atwhich 50% of 10 indents exhibit at least one radial/median crackemanating from the corners of the indent impression. The maximum load isincreased until the threshold is met for a given glass ceramic and/orthe precursor glass. All indentation measurements are performed at roomtemperature in 50% relative humidity.

Fracture toughness values described herein as measured by chevron notchshort bar methods known in the art and described in ASTM procedureE1304-97 (2014), entitled “Standard Test Method for Plane-Strain(Chevron-Notch) Fracture Toughness of Metallic Materials.” The contentsof ASTM E1304-97 (2014) are incorporated herein by reference in theirentirety. The test method involves application of a load to the mouth ofa chevron-notched specimen to induce an opening displacement of thespecimen mouth. Fracture toughness measured according to this method isrelative to a slowly advancing steady-state crack initiated at a chevronnotch and propagating in a chevron-shaped ligament.

Glass Ceramics and Glass Ceramic Precursors

When a glass is converted into a glass-ceramic, portions of the glasscrystallize while other portions may remain in a residual glass phase(e.g., amorphous, non-crystalline). As used herein, the term “glassceramic” refers to a material comprising at least one crystalline phaseand at least one residual glass phase. The amount of material in acrystalline phase or in crystalline phases is measured in wt %. Theweight fraction ratio of the crystalline phases may be determined bymethods known in the art, such as x-ray diffraction methods includingRietveld refinement. In some embodiments, a glass ceramic is a materialcomprising at least 30%, 50%, 60%, 70%, 75%, 80%, 85%, 90%, 95%, 97%,98%, 99% or greater than 99% w/w at least one crystalline phase, withthe remaining volume comprising a glass phase. In some embodiment, thematerial comprises from 50-98% glass ceramic phase, 60-98% glass ceramicphase, 70-98% glass ceramic phase, 80-98% glass ceramic phase, 80-95%glass ceramic phase, or 60-90% glass ceramic phase. The terms “glassceramic article” and “glass ceramic articles” are used in their broadestsense to include any object made wholly or partly of glass ceramic. Theterms “ceram” and “ceramming,” as used herein, refer to a heat treatment(or heat treatments) or other process(es) used to convert a precursorglass into a glass ceramic.

The glass ceramics described herein include crystalline structures thatcan be understood via crystallography and known crystal systems. As usedherein the terms “tetragonal ZrO₂,” “tetragonal zirconia,” and “t-ZrO₂”are used interchangeably and refer to crystalline ZrO₂ having atetragonal crystal system; the terms “monoclinic ZrO₂,” “monocliniczirconia,” and “m-ZrO₂” are used interchangeably and refer tocrystalline ZrO₂ having a monoclinic crystal system; and the term “cubicZrO₂” is used interchangeably and refer to crystalline ZrO₂ having acubic crystal system as understood in chemical crystallography. “Lithiumsilicate” phase may comprise lithium disilicates, monosilicates, andmetasilicates. Additional crystalline structures may be present in theprecursor glass or glass ceramic phases of the materials. For example,lithium disilicate glass ceramic phases may have orthorhombic or othercrystal systems.

A first aspect comprises zirconia-containing precursor glasses and glassceramics made from the precursor glasses. The glass ceramics made fromthese zirconia-containing precursor glasses are zirconia-toughened glassceramics having high weight fractions of tetragonal ZrO₂. While notbeing bound by theory, it is believed that the high levels of tetragonalZrO₂ allow for the glass ceramic to undergo phase transformation fromtetragonal ZrO₂ to monoclinic ZrO₂, greatly improving the materialsfracture toughness. Support for this theory is seen in the fact thatground powders made from these materials see increases in the amount ofmonoclinic ZrO₂ present. In some embodiments, the crystallinezirconia-containing glass ceramics may also comprise a lithium silicatephase. In some embodiments, the crystalline zirconia phase is tetragonalzirconia and the lithium silicate phase is lithium disilicate.

The precursor glass is capable of dissolving a large amount (generally,greater than about 10 wt %) of ZrO₂ without crystallizing upon coolingfrom the glass pour. Lithium and/or magnesium silicate melts withrelatively low alumina contents generally have high ZrO₂ solubility.When the precursor glass is subjected to a prescribed heat treatment,dissolved ZrO₂ is crystallized and precipitated out primarily as thetetragonal ZrO₂ phase with, in some embodiments, less than 5 wt %monoclinic ZrO₂ relative to the total ZrO₂.

The glass ceramics described herein comprise a tetragonal ZrO₂ phase, acrystalline lithium disilicate (Li₂Si₂O₅) phase, optionally a lithiumaluminosilicate phase and a residual glass phase. FIGS. 1A and 1Bprovide example micrographs of embodied glass ceramics comprising atetragonal ZrO₂ phase and a crystalline lithium disilicate (Li₂Si₂O₅)phase. The tetragonal ZrO₂ phase, in some embodiments, may comprise asignificant portion (40-95 wt %, 40-90 wt %, or 50-80 wt %) the ZrO₂present in the glass ceramic. In some embodiments, the tetragonal ZrO₂phase may comprise 5-25 wt % of the total glass ceramic composition(([weight tetragonal ZrO₂]/[weight of glass ceramic])*100). In someembodiments, the tetragonal ZrO₂ phase may comprise 5-60 wt %, 5-50 wt%, 5-40 wt %, 5-30 wt %, or 10-35 wt % of the total crystalline phase ofthe glass ceramic (([weight of tetragonal ZrO₂]/[weight of allcrystalline phases])*100). The tetragonal ZrO₂ phase may, in someembodiments, be dispersed throughout the residual glass phase. In otherembodiments, the crystalline t-ZrO₂ phase “decorates” or is near or incontact with the lithium disilicate phase such that the t-ZrO₂ andlithium disilicate phases may synergistically interact to provideimproved material properties. In some embodiments, the average crystalsize along the longest dimension for crystals of tetragonal ZrO₂ is from0.1 to 10 μm, 0.3 to 7 μm, 0.5 to 4 μm, 0.8 to 3 μm, or 0.5 to 3 μm.

The glass ceramic further comprises a lithium disilicate phase. In someembodiments, the lithium disilicate phase comprises about 25 to about 60wt % of the total glass ceramic composition. In some embodiments, thetetragonal ZrO₂ and lithium disilicate phases comprise 60-95 wt % of thetotal glass ceramic. In some embodiments, the lithium disilicate phasemay comprise 5-50 wt % of the total crystalline phase of the glassceramic. The lithium disilicate crystals may have a lath-like structure,with an aspect ratio of from about 1.5:1 to 12:1, 2:1 to 8:1 or greaterthan 2:1. In some embodiments, the average crystal size along thelongest dimension for crystals of lithium disilicate is at least 2 μm, 5μm, 8 μm, or 10 μm or from 1 to 20 μm, 2 to 15 μm, 5 to 20 μm, 5 to 15μm, 5 to 12 μm, 2 to 12 μm, 1 to 12 μm, 8 to 20 μm, or 10 to 20 μm.

In some embodiments, the glass ceramic further comprises one or moreadditional phases, such as lithium metasilicate, cubic zirconia,monoclinic ZrO₂, lithium aluminosilicate, β-spodumene solid solution,β-quartz solid solution, cristobalite, lithiophosphate, zekzerite,quartz solid solution, baddeleyite, lithium orthophosphate,(Na,Li)ZrSi₆O₁₈, or α-quartz phase or combinations thereof. In someembodiments, the additional phases comprise, in total, about 0-25 wt %of the glass ceramic.

The glass phase, in some embodiments, may comprise 1-50 wt %, 2-50 wt %,3-50 wt %, 5-40 wt %, 5-30 wt %, 5-20 wt %, 3-10 wt %, or 5-50 wt % ofthe total glass ceramic composition.

In some embodiments, the tetragonal ZrO₂/lithium disilicate glassceramic and/or the precursor glass used to form the glass ceramiccomprises at least 3 mol % ZrO₂ and 18 to 40 mol % Li₂O, 19 to 37 mol %Li₂O, 25 to 35 mol % Li₂O, or 30 to 35 mol % Li₂O. In some embodiments,the glass ceramic and/or the precursor glass used to form the glassceramic may comprise additional components. In some embodiments,additionally comprises 0 to 7 mol % Al₂O₃, 0 to 5 mol % Al₂O₃, 0 to 4mol % Al₂O₃, 0 to 3 mol % Al₂O₃, >0 to 7 mol % Al₂O₃, >0 to 5 mol %Al₂O₃, >0 to 4 mol % Al₂O₃, >0 to 3 mol % Al₂O₃, 0.5 to 7 mol % Al₂O₃,0.5 to 5 mol % Al₂O₃, 0.5 to 4 mol % Al₂O₃, or 0.5 to 3 mol % Al₂O₃.

In some embodiments, the glass ceramic may further include at least oneof crystalline cubic ZrO₂ or monoclinic ZrO₂ phases. In someembodiments, the glass ceramic may comprise a monoclinic ZrO₂ phase. Insuch instances, the ratio of weight fraction (or weight percentage) oftetragonal zirconia to that of monoclinic zirconia is at least about 8:1(i.e., tetragonal-ZrO₂(wt %)/monclinic-ZrO₂(wt %))≥8); in someembodiments, at least about 10:1 (tetragonal-ZrO₂(wt%)/monclinic-ZrO₂(wt %))≥10); in other embodiments, at least about 15(tetragonal-ZrO₂(wt %)/monclinic-ZrO₂(wt %))≥15); and in still otherembodiments, at least about 20 (tetragonal-ZrO₂(wt %)/monclinic-ZrO₂(wt%))≥20). In some embodiments the amount of monclinic-ZrO₂ in the glassceramic is from 0 to 5 wt %, >0 to 5 wt %, 0 to 3 wt %, 0 to 1 wt %, >0to 3 wt %, or >0 to 1 wt %. The weight fraction ratio of the tetragonalto monoclinic zirconia phases may be determined by those x-raydiffraction methods, such as Rietveld refinement, known in the art.

In some embodiments, the glass ceramic and/or the precursor glass usedto form the glass ceramic comprises a combination of SiO₂, Li₂O, ZrO₂,and optionally, Al₂O₃, alkali oxides, alkaline earth oxides, and rareearth oxides. For example, embodiments may comprise from 50 mol % to 75mol % SiO₂ (50 mol %≤SiO₂≤75 mol %); from 18 mol % to 40 mol % Li₂O (18mol %≤Li₂O ≤40 mol % Li₂O); from 3 mol % to 17 mol % ZrO₂ (3 mol%≤ZrO₂≤15 mol %); from 0 mol % to 5 mol % Al₂O₃ (0 mol %≤Al₂O₃≤5 mol %);from 0 mol % to 5 mol % Na₂O (0 mol %≤Na₂O ≤5 mol %); from greater than0 mol % to 14 mol % R₂O (0 mol %≤R₂O≤14 mol %), where R is the sum ofthe alkali metals Na, K, and Cs (not Li); from 0 mol % to 5 mol % of atleast one alkaline earth oxide (RO; R=Mg, Sr, Ca, Ba) (0 mol %≤RO≤5 mol%); from 0 mol % to 5 mol % of at least one transition metal oxide(“TMO”) (oxids of metals in groups IVB-VIII, IB, and IIB, or 4-12 in theperiodic table; e.g., Zn, Ti, Fe, etc.) (0 mol %≤RO≤5 mol %); and from 0mol % to 5 mol % of at least one rare earth oxide (“REO”)oxides ofscandium, yttrium, and the lanthanides) (0 mol %≤REO≤5 mol %).Additional aspects of the various constituents that can make up theembodied compositions are detailed below.

SiO₂, along with Al₂O₃, B₂O₃, P₂O₅, ZrO₂ and SnO₂, are network formerswhen present in the glass ceramic and/or the precursor glass. SiO₂,which is the largest oxide component of the glass ceramic and/or theprecursor glass, may be included to provide high temperature stabilityand chemical durability. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 50 to 75 mol % SiO₂. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 55 to 70 mol % SiO₂. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 57 to 65 mol % SiO₂. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 57 to 70 mol % SiO₂. In some embodiments, the glass ceramic and/orthe precursor glass can comprise 50 to 75 mol %, 50 to 70 mol %, 50 to65 mol %, 50 to 60 mol %, 55 to 75 mol %, 57 to 70 mol %, 57 to 65 mol%, 55 to 70 mol %, or 55 to 65 mol % SiO₂. In some embodiments, theglass ceramic and/or the precursor glass comprises 50, 51, 52, 53, 54,55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72,73, 74, or 75 mol % SiO₂.

Li₂O may provide the basis for the lithium disilicate phase. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 18 to 40 mol % Li₂O. In some embodiments, the glass ceramic and/orthe precursor glass can comprise 18 to 30 mol % Li₂O. In someembodiments, the glass ceramic and/or the precursor glass can comprise25 to 36 mol % Li₂O. In some embodiments, the glass ceramic and/or theprecursor glass can comprise 30 to 35 mol % Li₂O. In some embodiments,the glass ceramic and/or the precursor glass can comprise from 18 to 40mol %, 18 to 36 mol %, 18 to 30 mol %, 18 to 25 mol %, 20 to 40 mol %,20 to 36 mol %, 20 to 30 mol %, 20 to 25 mol %, 25 to 40 mol %, 25 to 36mol %, 25 to 30 mol %, 30 to 40 mol %, 30 to 36 mol %, or 36 to 40 mol%. In some embodiments, the glass ceramic and/or the precursor glass cancomprise 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33,34, 35, 36, 37, 38, 39, or 40 mol % Li₂O.

Zirconium dioxide or zirconia, ZrO₂, is the primary component of thetetragonal and other crystalline ZrO₂ phases. In some embodiments, theglass ceramic and/or the precursor glass can comprise at least 3 mol %ZrO₂ or, in some embodiments, from 3 to 25 mol % ZrO₂. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 4 to 20 mol % ZrO₂. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 6 to 15 mol % ZrO₂. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 3 to 25 mol %, 3 to 20 mol %, 3 to 18 mol %, 3 to 15 mol %, 3 to 12mol %, 3 to 10 mol %, 3 to 8 mol %, 4 to 25 mol %, 4 to 20 mol %, 4 to18 mol %, 4 to 15 mol %, 4 to 12 mol %, 4 to 10 mol %, 4 to 8 mol %, 6to 25 mol %, 6 to 20 mol %, 6 to 18 mol %, 6 to 15 mol %, 6 to 12 mol %,6 to 10 mol %, ZrO₂. In some embodiments, the glass ceramic and/or theprecursor glass can comprise 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 mol % ZrO₂.

Al₂O₃ may influence the structure of the precursor glass and/or theglass ceramic and, additionally, lower the liquidus temperature andcoefficient of thermal expansion, or enhance the strain point. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0 to 5 mol % Al₂O₃. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from >0 to 5 mol % Al₂O₃. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom about 0 to 3 mol % Al₂O₃ or >0 to 3 mol % Al₂O₃. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 1 to 4 mol % Al₂O₃. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 0 to 5 mol %, 0 to 4 mol %, 0 to 3mol %, 0 to 2 mol %, >0 to 5 mol %, >0 to 4 mol %, >0 to 3 mol %, >0 to2 mol %, 1 to 5 mol %, 1 to 4 mol %, or 1 to 3 mol % Al₂O₃. In someembodiments, the glass ceramic and/or the precursor glass can compriseabout 0, >0, 1, 2, 3, 4, or 5 mol % Al₂O₃.

Without being bound by theory, it is believed that limiting the contentof B₂O₃ in the glasses and glass ceramics described herein to 0 to 5 wt% helps provide a durable glass ceramic. In some embodiments, the glassceramic and/or the precursor glass can comprise from 0 to 5 mol % B₂O₃.In some embodiments, the glass ceramic and/or the precursor glass cancomprise from >0 to 5 mol % B₂O₃. In some embodiments, the glass ceramicand/or the precursor glass can comprise from about 0 to 3 mol % B₂O₃or >0 to 3 mol % B₂O₃. In some embodiments, the glass ceramic and/or theprecursor glass can comprise from 1 to 4 mol % B₂O₃. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0 to 5 mol %, 0 to 4 mol %, 0 to 3 mol %, 0 to 2 mol %, >0 to 5 mol%, >0 to 4 mol %, >0 to 3 mol %, >0 to 2 mol %, 1 to 5 mol %, 1 to 4 mol%, or 1 to 3 mol % B₂O₃. In some embodiments, the glass ceramic and/orthe precursor glass can comprise about 0, >0, 1, 2, 3, 4, or 5 mol %B₂O₃.

Phosphorous pentoxide, P₂O₅, may be present in order to stabilize thetetragonal ZrO₂. In some embodiments, the glass ceramic and/or theprecursor glass can comprise from >0 to 5 mol % P₂O₅. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0.2 to 5 mol % P₂O₅. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from about >0 to 3 mol % P₂O₅ or 0.2 to3 mol % P₂O₅. In some embodiments, the glass ceramic and/or theprecursor glass can comprise from 1 to 4 mol % P₂O₅. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0.2 to 5 mol %, 0.2 to 4 mol %, 0.2 to 3 mol %, 0.2 to 2 mol %, >0to 5 mol %, >0 to 4 mol %, >0 to 3 mol %, >0 to 2 mol %, 1 to 5 mol %, 1to 4 mol %, or 1 to 3 mol % P₂O₅. In some embodiments, the glass ceramicand/or the precursor glass can comprise about 0, >0, 1, 2, 3, 4, or 5mol % P₂O₅.

Rare earth oxides may be present in order to stabilize the tetragonalZrO₂. In some embodiments, the glass ceramic and/or the precursor glasscomprises from 0 mol % to 5 mol % of at least one rare earth oxide (REO;i.e., oxides of scandium, yttrium, and the lanthanides) (0 mol %≤REO≤5mol %). In some embodiments, the glass ceramic and/or the precursorglass comprises from greater than 0 mol % to 5 mol % of at least onerare earth oxide (REO; i.e., oxides of scandium, yttrium, and thelanthanides) (0 mol %≤REO≤5 mol %), where ‘greater than 0’ means anypositive value, such as 0.001 mol %. The glass ceramic and/or theprecursor glass may, in some embodiments, comprise from 0 mol % to 3 mol% or from greater than 0 mol % to 2 mol % Y₂O₃ (0 mol %≤Y₂O₃≤ 3 mol % or0 mol %<Y₂O₃≤ 2 mol %). In some embodiments, the ratio of Y₂O₃ (mol%)/ZrO₂(mol %) is less than 0.2, 0.15, 0.1, 0.05, or 0.1. In someembodiments, the glass ceramic and/or the precursor glass comprises from0 to 5 mol %, >0 to 5 mol %, 1 to 5 mol %, 2 to 5 mol %, 0 to 4 mol %, 0to 3 mol %, 0 to 2 mol %, 0 to 1 mol %, >0 to 4 mol %, >0 to 3 mol %, >0to 2 mol %, or >0 to 1 mol %, 0 to about 0.5 mol %, 0 to about 0.1 mol%, 0 to about 0.05 mol %, or 0 to about 0.01 mol % CeO₂.

Non-lithium alkali oxides may also be present in the glass ceramicand/or the precursor glass. In some embodiments, the glass ceramicand/or the precursor glass comprises from 0 mol % to about 14 mol % R₂O(0 mol %<R₂O≤14 mol %), where R is the sum of the alkali metals Na, K,Cs, and Rb (not Li), in the glass ceramic and/or the precursor glass. Insome embodiments, the glass ceramic and/or the precursor glass cancomprise from 0 to 10 mol % or 0 to 8 mol % R₂O. In some embodiments,the glass ceramic and/or the precursor glass can comprise from >0 to14, >0 to 10, or >0 to 8 mol % R₂O. In some embodiments, the glassceramic and/or the precursor glass can comprise 0.5 to 4 mol % R₂O. Insome embodiments, the glass ceramic and/or the precursor glass cancomprise from 0 to 14 mol %, 0 to 10 mol %, 0 to 8 mol %, 0 to 6 mol %,0 to 4 mol %, >0 to 14 mol %, >0 to 10 mol %, >0 to 8 mol %, >0 to 6 mol%, >0 to 4 mol %, 1 to 14 mol %, 1 to 10 mol %, 1 to 8 mol %, 1 to 6 mol%, 2 to 14 mol %, 2 to 10 mol %, 2 to 8 mol %, 2 to 6 mol %, 4 to 14 mol%, 4 to 10 mol %, 4 to 8 mol %, 6 to 14 mol %, 6 to 10 mol %, 8 to 14mol % or 8 to 10 mol % R₂O. In some embodiments, the glass ceramicand/or the precursor glass can comprise about 0, >0, 1, 2, 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, or 14 mol % R₂O.

Na₂O can be useful in the glass ceramic and/or the precursor glass forion exchange and chemical tempering. In some embodiments, the glassceramic and/or the precursor glass comprises from 0 mol % to about 5 mol% Na₂O (0 mol %≤Na₂O≤5 mol %). In some embodiments, the glass ceramicand/or the precursor glass can comprise from greater than 0 to 5 mol %Na₂O. In some embodiments, the glass ceramic and/or the precursor glasscan comprise from about 0 to 3 mol % Na₂O or >0 to 3 mol % Na₂O. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0.5 to 4 mol % Na₂O. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 0 to 5 mol %, 0 to 4 mol %, 0 to 3mol %, 0 to 2 mol %, >0 to 5 mol %, >0 to 4 mol %, >0 to 3 mol %, >0 to2 mol %, 1 to 5 mol %, 1 to 4 mol %, or 1 to 3 mol % Na₂O. In someembodiments, the glass ceramic and/or the precursor glass can compriseabout 0, >0, 1, 2, 3, 4, or 5 mol % Na₂O.

K₂O may also be useful in ion exchange and may be present in the glassceramic and/or the precursor glass at amounts from 0 mol % to about 10mol % K₂O (0 mol %<K₂O≤10 mol %). In some embodiments, the glass ceramicand/or the precursor glass can comprise from >0 to 10 mol % K₂O. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom about 0 to 5 mol % K₂O or >0 to 3 mol % K₂O. In some embodiments,the glass ceramic and/or the precursor glass can comprise from 0.5 to 4mol % K₂O. In some embodiments, the glass ceramic and/or the precursorglass can comprise from 0 to 10 mol %, 0 to 8 mol %, 0 to 5 mol %, 0 to4 mol %, 0 to 3 mol %, >0 to 10 mol %, >0 to 8 mol %, >0 to 5 mol %, >0to 3 mol %, 1 to 10 mol %, 1 to 8 mol %, 1 to 5, 1 to 4 mol %, 1 to 3mol %, 2 to 10 mol %, 2 to 8 mol %, or 2 to 4 K₂O. In some embodiments,the glass ceramic and/or the precursor glass can comprise about 0, >0,1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mol % K₂O.

In some embodiments, the precursor glasses and glass ceramics may be Csand Rb free. In such embodiments, the term R′₂O is used to distinguishfrom R₂O above, where R′ is the sum of the alkali metals Na and K, butdoes not include Cs, Li, and Rb. In some embodiments, the glass ceramicand/or the precursor glass comprises from 0 mol % to about 14 mol % R′₂O(0 mol %<R′₂O≤14 mol %). In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 0 to 10 mol % or 0 to 8 mol %R′₂O. In some embodiments, the glass ceramic and/or the precursor glasscan comprise from >0 to 14, >0 to 10, or >0 to 8 mol % R′₂O. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 1 to 4 mol % R′₂O. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 0 to 14 mol %, 0 to 10 mol %, 0 to8 mol %, 0 to 6 mol %, 0 to 4 mol %, >0 to 14 mol %, >0 to 10 mol %, >0to 8 mol %, >0 to 6 mol %, >0 to 4 mol %, 1 to 14 mol %, 1 to 10 mol %,1 to 8 mol %, 1 to 6 mol %, 2 to 14 mol %, 2 to 10 mol %, 2 to 8 mol %,2 to 6 mol %, 4 to 14 mol %, 4 to 10 mol %, 4 to 8 mol %, 6 to 14 mol %,6 to 10 mol %, 8 to 14 mol % or 8 to 10 mol % R′₂O. In some embodiments,the glass ceramic and/or the precursor glass can comprise about 0, >0,1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14 mol % R′₂O.

Alkaline earth oxides may provide advantages for ion exchange in theglass ceramic or precursor glass, along with improving other propertiesin the materials. In some embodiments, the glass ceramic and/or theprecursor glass comprises from 0 mol % to about 10 mol % MO (0 mol%<MO≤10 mol %), where M is the sum of the alkaline earth metals Mg, Ca,Sr, and Ba, in the glass ceramic and/or the precursor glass. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0 to 8 mol % MO. In some embodiments, the glass ceramic and/or theprecursor glass can comprise from 0 to 5 mol % MO. In some embodiments,the glass ceramic and/or the precursor glass can comprise from 1 to 8mol % MO. In some embodiments, the glass ceramic and/or the precursorglass can comprise from 0 to 10 mol %, 0 to 8 mol %, 0 to 6 mol %, 0 to4 mol %, 1 to 10 mol %, 1 to 8 mol %, 1 to 6 mol % 2 to 10 mol %, 2 to 8mol %, or 2 to 6 mol % MO. In some embodiments, the glass ceramic and/orthe precursor glass can comprise about >0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or10 mol % MO.

Titanium dioxide, TiO₂, can provide improved fracture toughness to theglass ceramic and/or the precursor glass, either alone or in combinationwith the tetragonal ZrO₂. In some embodiments, the glass ceramic and/orthe precursor glass may further comprise from 0 mol % to about 10 mol %TiO₂, >0 mol % to about 10 mol % TiO₂, 0 mol % to about 5 mol % TiO₂,or >0 mol % to about 5 mol % TiO₂. In some embodiments, the glassceramic and/or the precursor glass may comprise 0 to 5 mol %, 0 to 4 mol%, 0 to 3 mol %, 0 to 2 mol %, 0 to 1 mol %, >0 to 10 mol %, >0 to 5 mol%, >0 to 4 mol %, >0 to 3 mol %, >0 to 2 mol %, >0 to 1 mol %, 0.01 to 3mol %, or 0.1 to 2 mol % TiO₂.

ZnO may be present in the glass ceramic and/or the precursor glass. Insome embodiments, the glass ceramic and/or the precursor glass comprisesfrom 0 mol % to about 5 mol % ZnO (0 mol %<ZnO≤5 mol %). In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom greater than 0 to 5 mol % ZnO. In some embodiments, the glassceramic and/or the precursor glass can comprise from about 0 to 3 mol %ZnO or >0 to 3 mol % ZnO. In some embodiments, the glass ceramic and/orthe precursor glass can comprise from 0.5 to 4 mol % ZnO. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0 to 5 mol %, 0 to 4 mol %, 0 to 3 mol %, 0 to 2 mol %, >0 to 5 mol%, >0 to 4 mol %, >0 to 3 mol %, >0 to 2 mol %, 1 to 5 mol %, 1 to 4 mol%, or 1 to 3 mol % ZnO. In some embodiments, the glass ceramic and/orthe precursor glass can comprise about 0, >0, 1, 2, 3, 4, or 5 mol %ZnO.

In some embodiments, the glass ceramics above further comprise acoloring component. The coloring component may comprise, for example,Fe₂O₃, V₂O₅, Cr₂O₃, TiO₂, MnO₂, NiO, ZnO, CuO, NiO, Co₃O₄, rare earthoxides, and combinations thereof. In some cases, the total mol % ofcoloring component is from 0 to 4 mol %, 0 to 3 mol %, 0 to 2 mol %, 0to 1 mol %, >0 to 1, >0 to 2, >0 to 3, or >0 to 4 mol %.

Additional components can be incorporated into the glass ceramic and/orthe precursor glass to provide additional benefits or may beincorporated as contaminants typically found in commercially-preparedglass. For example, additional components can be added as fining agents(e.g., to facilitate removal of gaseous inclusions from melted batchmaterials used to produce the glass) and/or for other purposes. In someembodiments, the glass ceramic and/or the precursor glass may compriseone or more compounds useful as ultraviolet radiation absorbers. In someembodiments, the glass ceramic and/or the precursor glass can comprise 3mol % or less MnO, Nb₂O₅, MoO₃, Ta₂O₅, WO₃, SnO₂, Fe₂O₃, As₂O₃, Sb₂O₃,Cl, Br, or combinations thereof. In some embodiments, the glass ceramicand/or the precursor glass can comprise from 0 to about 3 mol %, 0 toabout 2 mol %, 0 to about 1 mol %, 0 to 0.5 mol %, 0 to 0.1 mol %, 0 to0.05 mol %, or 0 to 0.01 mol % MnO, ZnO, Nb₂O₅, MoO₃, Ta₂O₅, WO₃, SnO₂,Fe₂O₃, As₂O₃, Sb₂O₃, Cl, Br, or combinations thereof. In someembodiments, the glass ceramic and/or the precursor glass can comprisefrom 0 to about 3 mol %, 0 to about 2 mol %, 0 to about 1 mol %, 0 toabout 0.5 mol %, 0 to about 0.1 mol %, 0 to about 0.05 mol %, or 0 toabout 0.01 mol % SnO₂ or Fe₂O₃, or combinations thereof. The glasses,according to some embodiments, can also include various contaminantsassociated with batch materials and/or introduced into the glass by themelting, fining, and/or forming equipment used to produce the glass.

Non-limiting examples of precursor glasses for forming the embodiedglass ceramics are listed in Table 1, wherein the values of thecomponents are listed in mol %.

TABLE 1 Sample A B C D E F G H I J K L M SiO₂ 55 55 55 55 55 55 55 55 5555 55 55 55 ZrO₂ 3 3 5 5 10 10 13 15 17 20 20 25 25 Li₂O 40 25 18 30 2032 25 20 18 18 20 18 18 Na₂O 1 5 4 2 1.5 2 1 0.5 2 4 1.5 1 1 K₂O 0 0 1 22.5 0 4 7.5 0 0.5 0 0 0 MO* 0 4 8 1 7 0 0.5 0 1 0 1 0 0 Al₂O₃ 0.5 2 4 30 0 1 0.5 0.5 0 0.5 0 0.5 B₂O₃ 0 1 1 0.5 0 0 0 0 0 2 0 0 0 P₂O₅ 0.5 21.5 0.5 4 1 0.5 1 2.5 0.5 1 0.75 0.5 REO 0 2 0.5 1 0 0 0 0 4 0 0 0.25 0Other 0 TiO₂ ZnO 0 0 0 0 Cs₂O 0 0 CO₃O₄ 0 0 1 2 0.5 1 Sample N O P Q R ST U V W X Y Z SiO₂ 60 60 60 60 60 60 58 58 60 60 59 65 65 ZrO₂ 3 3 5 5 910 13 15 17 20 20 3 3 Li₂O 34 25 18 25 18 27 22 20 18 18 18 18 18 Na₂O 13 4 2 1.5 2 1 0 0 1 1.25 1 5 K₂O 0 0 3 2 0.5 0 3 5 0 0.4 0 7 0 MO* 1 2 81 7 0 0.5 0 0 0 0 1.5 0 Al₂O₃ 0.5 2 0 3 0 0 0 0.5 0.5 0 0.25 0 5 B₂O₃ 01 0 0.5 0 0 0 0 0 0.5 0 0 0 P₂O₅ 0.5 2 1.5 0.5 4 1 0.5 1.5 0.5 0.1 1 4 3REO 0 2 0.5 1 0 0 0 0 4 0 0 0.5 1 Other 0 0 0 0 0 0 TiO₂ 0 0 0 Rb₂O 0 02 0.5 Sample AA AB AC AD AE AF AG AH AI AJ AK AL AM SiO₂ 65 65 64 65 6465 65 70 69 70 70 70 70 ZrO₂ 3 5 5 9 10 13 15 3 3 3 5 5 9 Li₂O 30 20 2418 24 20 18 20 18 20 20 23 20 Na₂O 1 4 0.5 3 1 0.3 0.7 2 2 1.5 2.5 1.50.5 K₂O 0 1 1.8 0.5 0 0.2 0.3 1 0 0 0 0 0 MO* 0 1 0 0.5 0 1 0 0.5 5 20.7 0 0 Al₂O₃ 0.5 2 1 2 0 0 0.3 1 1 1 0 0 0 B₂O₃ 0 0 0.6 0 0 0 0 0.5 0 01 0 0 P₂O₅ 0.5 1.8 3 1 1 0.5 0.5 2 1 2.5 1.5 1 0.5 REO 0 0.2 0.1 0 0 00.2 0 0 0 0.3 0 0 *MO = CaO + MgO + SrO + BaO

As noted above, the glass ceramic described herein comprise a tetragonalZrO₂ crystalline phase and a lithium disilicate phase. In someembodiments, the glass ceramics described herein may also contain othersecondary crystalline phases. Such phases may be beneficial fortoughening or for chemical strengthening by ion exchange processes knownin the art (as is the case for β-spodumene solid solutions or glass). Insome cases, the crystalline phases are interlocked or the crystals arevery close together, leaving an intermixed glass phase. These uniquemicrostructures and phase assemblages are not available usingtraditional ceramic processing routes—the disclosed method gives thesemicrostructures by homogenous nucleation of the precursor glass thatresults in the disclosed phase assemblages and microstructures withoutthe use of high temperature sintering or the hazard of inhomogeneousdispersion of a ZrO₂ phase in molten glass. Additionally, certain phasesmay also serve to decrease the coefficient of thermal expansion (CTE) ofthe glass ceramic material. Accordingly, the glass ceramic may furthercomprise at least one of a lithium aluminosilicate phase, a cristobalitephase, a β-spodumene phase, a lithiophosphate (Li₃PO₄) crystallinephase, a crystalline lithium orthophosphate phase, a quartz solidsolution phase, a baddeleyite phase, a lithium metasilicate (Li₂SiO₃)phase, a monoclinic zirconia phase, a zekzerite phase, a cubic zirconiaphase, or a crystalline (Na,Li)ZrSi₆O₁₈ phase. As used herein the term“quartz solid solution” includes solid solutions of SiO₂ and up to about50 wt % Li(AlO₂).

Non-limiting examples of embodied ranges for glass ceramics are listedin Table 2, wherein the values of the components are listed in mol %.

Sample I II III IV SiO₂ 50-80 55-70 58-69 50-80 Al₂O₃ 0-5 0-5 0-5 0-5B₂O₃ 0-5 0-5 0-5 0-5 Li₂O 18-40 18-40 18-40 18-30 Na₂O 0-5 0-5 0-5 0-5MO  0-10  0-10  0-10  0-10 ZnO 0-5 0-5 0-5 0-5 ZrO₂ 1.5-25  1.5-25 1.5-25  1.5-25  P₂O₅ >0-5  >0-5  >0-5  >0-5  REO 0-5 0-5 0-5 0-5Ceramming One of C1-C4    cycle Phase           t-ZrO₂, lithiumdisilicate, assemblage plus minor phases including         m-ZrO₂,cristobalite, lithiophosphate, zektzerite Sample V VI VII VIII SiO₂55-70 58-69 50-80 55-70 Al₂O₃ 0-5 0-5 0-5 0-5 B₂O₃ 0-5 0-5 0-5 0-5 Li₂O18-30 18-30 25-36 25-36 Na₂O 0-5 0-5 0-5 0-5 MO  0-10  0-10  0-10  0-10ZnO 0-5 0-5 0-5 0-5 ZrO₂ 1.5-25  1.5-25  1.5-25  1.5-25 P₂O₅ >0-5  >0-5  >0-5  >0-5  REO 0-5 0-5 0-5 0-5 Ceramming One ofC1-C4    cycle Phase           t-ZrO₂, lithium disilicate, assemblageplus minor phases including         m-ZrO₂, cristobalite,lithiophosphate, zektzerite Sample IX X XI XII SiO₂ 58-69 55-70 58-6955-70 Al₂O₃ 0-5 0-5 0-5 0-5 B₂O₃ 0-5 0-5 0-5 0-5 Li₂O 25-36 18-40 18-4018-40 Na₂O 0-5 0-5 0-5 0-5 MO  0-10  0-10  0-10  0-10 ZnO 0-5 0-5 0-50-5 ZrO₂ 1.5-25   4-20  4-20  6-15 P₂O₅ >0-5  >0-5  >0-5  >0-5  REO 0-50-5 0-5 0-5 Ceramming One of C1-C4    cycle Phase           t-ZrO₂,lithium disilicate, assemblage plus minor phases including        m-ZrO₂, cristobalite, lithiophosphate, zektzerite Sample XIIIXIV XV XVI SiO₂ 58-69 55-70 58-69 50-80 Al₂O₃ 0-5 0-5 0-5 0-5 B₂O₃ 0-50-5 0-5 0-5 Li₂O 18-40 18-40 18-40 18-30 Na₂O 0-5 0-5 0-5 0-5 MO  0-10 0-10  0-10  0-10 ZnO 0-5 0-5 0-5 0-5 ZrO₂  6-15 1.5-25  1.5-25   4-20P₂O₅ >0-5  0.2-5  0.2-5  >0-5  REO 0-5 0-5 0-5 0-5 Ceramming One ofC1-C4    cycle Phase           t-ZrO₂, lithium disilicate, assemblageplus minor phases including         m-ZrO₂, cristobalite,lithiophosphate, zektzerite Sample XVII XVIII XIX XX SiO₂ 50-80 50-8050-80 55-70 Al₂O₃ 0-5 0-5 0-5 0-5 B₂O₃ 0-5 0-5 0-5 0-5 Li₂O 25-36 18-3025-36 18-30 Na₂O 0-5 0-5 0-5 0-5 MO  0-10  0-10  0-10  0-10 ZnO 0-5 0-50-5 0-5 ZrO₂  4-20  6-15  6-15  4-20 P₂O₅ >0-5  >0-5  >0-5  >0-5  REO0-5 0-5 0-5 0-5 Ceramming One of C1-C4    cycle Phase           t-ZrO₂,lithium disilicate, assemblage plus minor phases including        m-ZrO₂, cristobalite, lithiophosphate, zektzerite Sample XXIXXII XXIII XIV SiO₂ 55-70 58-69 58-69 58-69 Al₂O₃ 0-5 0-5 0-5 0-5 B₂O₃0-5 0-5 0-5 0-5 Li₂O 25-36 18-30 25-36 18-30 Na₂O 0-5 0-5 0-5 0-5 MO 0-10  0-10  0-10  0-10 ZnO 0-5 0-5 0-5 0-5 ZrO₂  6-15  4-20  6-15  6-15P₂O₅ >0-5  >0-5  >0-5  0.2-5  REO 0-5 0-5 0-5 0-5 Ceramming One ofC1-C4    cycle Phase           t-ZrO₂, lithium disilicate, assemblageplus minor phases including         m-ZrO₂, cristobalite,lithiophosphate, zektzerite C1: 2 hr at 700° C., 4 hr at 850° C. (±1hour; ±25° C. for each) C2: 2 hr at 700° C., 4 hr at 875° C. (±1 hour;±25° C. for each) C3: 2 hr at 750° C., 4 hr at 900° C. (±1 hour; ±25° C.for each) C4: 2 hr at 800° C., 4 hr at 900° C. (±1 hour; ±25° C. foreach)

In addition to having high fracture toughness, the glass ceramicsdescribed herein can have color and transparency/translucency propertiesthat make them advantageous for a number of applications. The glassceramics of one or more embodiments may exhibit a substantially white,“pearl,” milky, or white-translucent color. In some embodiments, theglass ceramics exhibit a color presented in CIELAB color spacecoordinates (determined from reflectance spectra measurements using aspectrophotometer, with illuminant D65 and specular reflectanceexcluded), of the following ranges: a*=from about −1 to about +3;b*=from about −7 to about +3; and L*>85. In some applications, the glassceramics are translucent and quantitatively white to yellow-brown incolor and are of particular interest in dental applications. In suchapplications, it may be desirable to have glass ceramics with CIELABcolor space coordinates: a*=from about −1 to about 1; b*=from about −4to about 1; and L*<60. In some embodiments, the glass ceramics arequalitatively described as white and opaque and have a color presentedin CIELAB color space coordinates: a*=from about 1 to about 0; b*=fromabout −2 to about 0; and L*>88. In some embodiments, the glass ceramicsare qualitatively described as black and opaque and have a colorpresented in CIELAB color space coordinates: a*=from about −1 to about1; b*=from about −1 to about 1; and L*<40.

Non-limiting examples of precursor glasses and glass ceramiccompositions, heat treatment (ceramming) schedules, and phaseassemblages resulting from different ceramming/heat treatment schedulesare listed in Table 3. Table 3 also includes comments regarding thegeneral appearance of the formed glass ceramic.

TABLE 3 Examples of precursor compositions (expressed in mol %),ceramming schedules, and phase assemblages resulting from different heattreatment schedules. Example 1 2 3 4 SiO₂ 67.0 63.9 61.1 58.5 Al₂O₃ 0 00 0 Li₂O 27.2 25.9 24.8 23.7 Na₂O 1.5 1.4 1.3 1.3 MgO 0 0 0 0 ZnO 0 0 00 CaO 0 0 0 0 ZrO₂ 2.9 7.4 11.5 15.3 P₂O₅ 1.5 1.4 1.3 1.3 Y₂O₃ 0 0 0 0SnO₂ 0 0 0 0 Ceramming 2 hr at 750° C., 2 hr at 750° C., 2 hr at 800°C., 2 hr at 700° C., cycle 4 hr at 900° C. 4 hr at 900° C. 4 hr at 900°C. 4 hr at 850° C. Phase lithium disilicate, lithium disilicate, t-ZrO₂,glass assemblage cristobalite, quartz, lithium disilicate,lithiophosphate cristobalite, cristobalite, lithiophosphate baddeleyite,lithiophosphate Appearance Translucent Translucent Opaque Transparentwhite white white Fracture 3.88 5.25 6.13 toughness (MPa · m^(1/2))Example 5 6 7 8 SiO₂ 57.3 54.1 57.3 56.2 Al₂O₃ 0 0 0 0 Li₂O 34.0 32.134.0 33.3 Na₂O 1.5 1.4 1.5 1.4 MgO 0 0 0 0 ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂5.8 11.0 5.8 7.6 P₂O₅ 1.5 1.4 1.5 1.4 Y₂O₃ 0 0 0 0 SnO₂ 0 0 0 0Ceramming 2 hr at 700° C., 2 hr at 700° C., 2 hr at 750° C., 2 hr at700° C., cycle 4 hr at 850° 4 hr at 850° C. 4 hr at 850° C. 4 hr at 875°C. Phase t-ZrO₂, t-ZrO₂, t-ZrO₂, t-ZrO₂, assemblage lithium disilicate,lithium metasilicate, lithium disilicate, lithium disilicate, lithiummetasilicate, cristobalite, lithium metasilicate, lithium metasilicate,baddeleyite, baddeleyite, baddeleyite, baddeleyite, lithiophosphatelithiophosphate lithiophosphate lithiophosphate Appearance Opaque OpaqueOpaque Opaque white white white white Fracture 2.73 2.36 3.00 3.8toughness (MPa · m^(1/2)) Flexural 556 500 strength (MPa) Ceramming 2 hrat 700° C., 2 hr at 700° C., 2 hr at 750° C., 2 hr at 750° C., cycles 4hr at 850° C. 4 hr at 850° C. 4 hr at 900° C. 4 hr at 900° C. Fracture3.90 5.30 toughness (MPa · m^(1/2)) Example 9 10 11 12 SiO₂ 55.1 54.162.1 59.3 Al₂O₃ 0 0 0 0 Li₂O 32.7 32.1 30.1 28.7 Na₂O 1.4 1.4 1.5 1.4MgO 0 0 0 0 ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 9.3 11.0 4.9 9.3 P₂O₅ 1.4 1.41.5 1.4 Y₂O₃ 0 0 0 0 SnO₂ 0 0 0 0 Ceramming 2 hr at 700° C., 2 hr at700° C., 2 hr at 700° C., 2 hr at 700° C., cycle 4 hr at 850° C. 4 hr at850° C. 4 hr at 850° C. 4 hr at 850° C. Phase t-ZrO₂, t-ZrO₂, t-ZrO₂,t-ZrO₂, assemblage lithium disilicate, lithium disilicate, lithiumdisilicate, lithium disilicate, lithium metasilicate, lithiummetasilicate, Baddeleyite, lithium metasilicate, baddeleyite,baddeleyite, lithiophosphate baddeleyite, lithiophosphatelithiophosphate cristobalite, lithiophosphate Appearance Opaque OpaqueOpaque Opaque white white white white Fracture 3.77 2.28 3.15 toughness(MPa · m^(1/2)) Flexural 191 strength (MPa) Ceramming 2 hr at 750° C., 2hr at 750° C., 2 hr at 700° C., 2 hr at 700° C., cycles 6 hr at 900° C.4 hr at 900° C. 4 hr at 850° C. 4 hr at 850° C. Fracture 7.93 6.10toughness (MPa · m^(1/2)) Example 13 14 15 16 SiO₂ 59.5 60.3 63.5 64.9Al₂O₃ 0 0 0 0 Li₂O 29.7 30.3 27.8 26.7 Na₂O 1.4 1.3 1.2 1.2 MgO 0 0 0 0ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 7.7 6.9 6.3 6.1 P₂O₅ 1.4 1.3 1.2 1.1 Y₂O₃0.2 0 0 0 SnO₂ 0 0 0 Ceramming 2 hr at 700° C., 2 hr at 700° C., 2 hr at700° C., 2 hr at 700° C., cycle 4 hr at 875° C. 4 hr at 875° C. 4 hr at875° C. 4 hr at 875° C. Phase t-ZrO₂, m-ZrO₂, t-ZrO₂, m-ZrO₂, t-ZrO₂,m-ZrO₂, t-ZrO₂, SiO₂, ZrSiO₄, assemblage lithium disilicate lithiumdisilicate lithium disilicate lithium disilicate quartz s.s., SiO₂,SiO₂, cristobalite SiO₂, lithiophosphate cristobalite lithiophosphate,lithiophosphate lithiophosphate, lithium metasilicate, lithiummetasilicate, NaLiZrSi₆O₁₈ NaLiZrSi₆O₁₈ Appearance white opaque, white,opaque, layered, layered, medium grained fine grained broken up brokenup on ceramming on ceramming Example 17 18 19 20 SiO₂ 66.2 67.4 68.569.5 A1₂O₃ 0 0 0 0 Li₂O 25.7 24.8 24 23.2 Na₂O 1.1 1.1 1 1 MgO 0 0 0 0ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 5.9 5.7 5.5 5.3 P₂O₅ 1.1 1.1 1 1 Y₂O₃ 0 0 00 SnO₂ 0 0 0 0 Ceramming 2 hr at 700° C., 2 hr at 700° C., 2 hr at 700°C., 2 hr at 700° C., cycle 4 hr at 875° C. 4 hr at 875° C. 4 hr at 875°C. 4 hr at 875° C. Phase t-ZrO₂, m-ZrO₂, t-ZrO₂, m-ZrO₂, t-ZrO₂, m-ZrO₂,t-ZrO₂, m-ZrO₂, assemblage lithium disilicate lithium disilicate lithiumdisilicate lithium disilicate cristobalite cristobalite cristobalitecristobalite lithiophosphate lithiophosphate lithiophosphatelithiophosphate zektzerite Appearance white, opaque, white opaque, whiteopaque, broke up fine grained fine to medium fine to medium onceramming, grain grain flaky Example 21 22 23 24 SiO₂ 70.5 71.4 72.362.1 Al₂O₃ 0 0 0 0 Li₂O 22.4 21.7 21.1 29.7 Na₂O 1 0.9 0.9 1.3 MgO 0 00.0 0 ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 5.1 5 4.8 5.6 P₂O₅ 1 0.9 0.9 1.4 Y₂O₃0 0 0 0 SnO₂ 0 0 0 0 Ceramming 2 hr at 700° C., 2 hr at 700° C., 2 hr at700° C., 2 hr at 700° C., cycle 4 hr at 875° C. 4 hr at 875° C. 4 hr at875° C. 4 hr at 875° C. Phase t-ZrO₂, m-ZrO₂, t-ZrO₂, m-ZrO₂, t-ZrO₂,m-ZrO₂, t-ZrO₂, m-ZrO₂, assemblage lithium disilicate lithium disilicatelithium disilicate lithium disilicate cristobalite cristobalitecristobalite cristobalite lithiophosphate lithiophosphatelithiophosphate lithiophosphate zektzerite zektzerite zektzeriteAppearance white opaque, white opaque, white white fine to medium fineto medium opaque opaque grain grain Example 25 26 27 28 SiO₂ 71.4 72.362.1 63.4 Al₂O₃ 0 0 0 0 Li₂O 21.7 21.1 29.7 29.4 Na₂O 0.9 0.9 1.3 1.3MgO 0 0 0 0 ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 5 4.8 5.6 4.6 P₂O₅ 0.9 0.9 1.41.3 Y₂O₃ 0 0 0 0 SnO₂ 0 0 0 0 Ceramming 2 hr at 700° C., 2 hr at 700°C., 2 hr at 700° C., 2 hr at 700° C., cycle 4 hr at 875° C. 4 hr at 875°C. 4 hr at 875° C. 4 hr at 875° C. Phase t-ZrO₂, m-ZrO₂, t-ZrO₂, m-ZrO₂,lithium disilicate t-ZrO₂, m-ZrO₂, assemblage lithium disilicate lithiumdisilicate cristobalite lithium disilicate cristobalite cristobalitelithiophosphate cristobalite lithiophosphate lithiophosphatelithiophosphate Appearance white white white opaque opaque translucentExample 29 30 31 32 SiO₂ 64.6 65.8 68.4 69.7 Al₂O₃ 0 0 0 0 Li₂O 29.128.8 24.0 23.7 Na₂O 1.3 1.3 1.1 1.1 MgO 0 0 0 0 ZnO 0 0 0 0 CaO 0 0 0 0ZrO₂ 3.7 2.8 5.5 4.5 P₂O₅ 1.3 1.3 1.0 1.0 Y₂O₃ 0 0 0 0 SnO₂ 0 0 0 0Ceramming 2 hr at 700° C., 2 hr at 700° C., 2 hr at 700° C., 2 hr at700° C., cycle 4 hr at 875° C. 4 hr at 875° C. 4 hr at 875° C. 4 hr at875° C. Phase t-ZrO₂, m-ZrO₂, t-ZrO₂, m-ZrO₂, t-ZrO₂, m-ZrO₂, t-ZrO₂,m-ZrO₂, assemblage lithium disilicate lithium disilicate lithiumdisilicate lithium disilicate cristobalite cristobalite cristobalitecristobalite lithiophosphate lithiophosphate lithiophosphatelithiophosphate Appearance Example 33 34 35 36 SiO₂ 70.9 70.1 70 70Al₂O₃ 0 0.5 0.8 1 Li₂O 23.5 23.2 23.2 23.2 Na₂O 1.1 0.9 0.9 0.9 MgO 0 00 0 ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 3.5 4.3 4.1 3.8 P₂O₅ 1 1 1 1 Y₂O₃ 0 0 00 SnO₂ 0 0 0 0 Ceramming 2 hr at 700° C., 2 hr at 700° C., 2 hr at 700°C., 2 hr at 700° C., cycle 4 hr at 875° C. 4 hr at 875° C. 4 hr at 875°C. 4 hr at 875° C. Phase t-ZrO₂, m-ZrO₂, t-ZrO₂, α-quartz m-ZrO₂,t-ZrO₂, α-quartz m-ZrO₂, t-ZrO₂, α-quartz m-ZrO₂, assemblage lithiumdisilicate lithium disilicate lithium disilicate lithium disilicatecristobalite cristobalite cristobalite cristobalite lithiophosphatelithiophosphate lithiophosphate lithiophosphate Appearance Example 37 3839 40 SiO₂ 70.3 70.1 69.9 69.6 Al₂O₃ 1 1.3 1.6 1.35 Li₂O 23.3 23.2 23.223.4 Na₂O 0 0 0 0.94 MgO 0 0 0 0 ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 4.3 4.34.3 3.58 P₂O₅ 1 1 1 1 Y₂O₃ 0 0 0 0 SnO₂ 0 0 0 0.08 Ceramming 2 hr at700° C., 2 hr at 700° C., 2 hr at 700° C., 2 hr at 700° C., cycle 4 hrat 875° C. 4 hr at 875° C. 4 hr at 875° C. 4 hr at 875° C. Phase t-ZrO₂,α-quartz m-ZrO₂, t-ZrO₂, α-quartz m-ZrO₂, t-ZrO₂, α-quartz m-ZrO₂,t-ZrO₂, α-quartz m-ZrO₂, assemblage lithium disilicate lithiumdisilicate lithium disilicate lithium disilicate cristobalitecristobalite cristobalite cristobalite lithiophosphate lithiophosphatelithiophosphate lithiophosphate Appearance Example 41 42 43 44 SiO₂ 69.669.72 70.59 70.65 Al₂O₃ 1.45 2.67 3.81 4.27 Li₂O 23.42 23.33 22.22 22.06Na₂O 0.9 0.45 0.17 0.06 MgO 0 0 0 0 ZnO 0 0 0 0 CaO 0 0 0 0 ZrO₂ 3.532.81 2.22 1.97 P₂O₅ 1.0 0.91 0.86 0.85 Y₂O₃ 0 0 0 0 SnO₂ 0.08 0.08 0.080.08 Ceramming 2 hr at 700° C., 2 hr at 700° C., 2 hr at 700° C., 2 hrat 700° C., cycle 4 hr at 875° C. 4 hr at 875° C. 4 hr at 875° C. 4 hrat 875° C. Phase t-ZrO₂, α-quartz t-ZrO₂, α-quartz β-spodumene t-ZrO₂,β-spodumene t-ZrO₂, assemblage β-spodumene m-ZrO₂, β-spodumene m-ZrO₂,α-quartz m-ZrO₂, α-quartz m-ZrO₂, lithium disilicate lithium disilicatelithium disilicate lithium disilicate cristobalite cristobalitecristobalite cristobalite lithiophosphate lithiophosphatelithiophosphate lithiophosphate Appearance Example 45 46 47 48 SiO₂ 68.664.1 56.2 56.2 Al₂O₃ 1.3 0.0 0 0 Li₂O 22.7 22.4 29.5 32 Na₂O 0.9 1.0 1.41.4 MgO 1.0 0.0 0 0 ZnO 1.0 0.0 0 0 CaO 0 6.4 3.8 0 ZrO₂ 3.5 5.1 7.6 7.6P₂O₅ 1.0 1.0 1.4 1.4 Y₂O₃ 0 0 0 0.9 SnO₂ 0 0 0 0 Ceramming 2 hr at 700°C., 2 hr at 700° C., cycle 4 hr at 875° C. 4 hr at 875° C. Phase t-ZrO₂,α-quartz m-ZrO₂, m-ZrO₂, assemblage lithium disilicate lithiumdisilicate lithiophosphate lithiophosphate lithium metasilicatezektzerite Appearance Example 49 50 51 52 SiO₂ 60.3 61.3 60.3 61.3 B₂O₃0 1 2 2 Li₂O 30.3 30.3 30.3 30.3 Na₂O 1.3 1.3 1.3 1.3 MgO 0 0 0 0 ZnO 00 0 0 CaO 0 0 0 0 ZrO₂ 6.9 4.9 4.9 3.9 P₂O₅ 1.3 1.3 1.3 1.3 Y₂O₃ 0 0 0 0SnO₂ 0 0 0 0 Phase t-ZrO₂, t-ZrO₂, t-ZrO₂, t-ZrO₂, assemblage lithiumdisilicate lithium disilicate lithium disilicate lithium disilicateCeramming 2 hr at 750° C., 2 hr at 750° C., 2 hr at 750° C., 2 hr at750° C., cycle 4 hr at 850° C. 4 hr at 850° C. 4 hr at 850° C. 4 hr at850° C. Appearance Smooth, semi glassy Course white Smooth, fine, glassywhite white Ceramming 2 hr at 750° C., 2 hr at 750° C., 2 hr at 750° C.,2 hr at 750° C., cycle 4 hr at 875° C. 4 hr at 875° C. 4 hr at 875° C. 4hr at 875° C. Appearance Less glassy than Course white Smooth, fine,glassy 850 white Ceramming 2 hr at 750° C., 2 hr at 750° C., 2 hr at750° C., 2 hr at 750° C., cycle 4 hr at 900° C. 4 hr at 900° C. 4 hr at900° C. 4 hr at 900° C. Appearance Less glassy than Course white Smooth,fine, glassy 850 white Example 53 54 55 56 SiO₂ 62.3 60.3 61.3 62.3 B₂O₃1 1.3 2.3 2 Li₂O 30.3 30.3 30.3 30.3 Na₂O 1.3 0 0 1.3 MgO 0 0 0 0 ZnO 00 0 0 CaO 0 0 0 0 ZrO₂ 3.9 6.9 4.9 2.9 P₂O₅ 1.3 1.3 1.3 1.3 Y₂O₃ 0 0 0 0SnO₂ 0 0 0 0 Phase t-ZrO₂, t-ZrO₂, t-ZrO₂, lithium disilicate assemblagelithium disilicate lithium disilicate lithium disilicate Ceramming 2 hrat 750° C., 2 hr at 750° C., 2 hr at 750° C., 2 hr at 750° C., cycle 4hr at 850° C. 4 hr at 850° C. 4 hr at 850° C. 4 hr at 850° C. AppearanceSmooth, courser Fine, less glassy Fine, less glassy Glassy, than #52than #50 than #50 translucent Ceramming 2 hr at 750° C., 2 hr at 750°C., 2 hr at 750° C., 2 hr at 750° C., cycle 4 hr at 875° C. 4 hr at 875°C. 4 hr at 875° C. 4 hr at 875° C. Appearance Smooth, higher Fine, lessglassy Fine, slightly more Glassy, coarseness than 850 than #50 coursethan #54 translucent Ceramming 2 hr at 750° C., 2 hr at 750° C., 2 hr at750° C., 2 hr at 750° C., cycle 4 hr at 900° C. 4 hr at 900° C. 4 hr at900° C. 4 hr at 900° C. Appearance Smooth, higher Medium grain Fine,slightly more Glassy, coarseness than 875 course than #54 translucentExample 57 58 SiO₂ 61.3 63.3 B₂O₃ 3 1 Li₂O 30.3 30.3 Na₂O 1.3 1.3 MgO 00 ZnO 0 0 CaO 0 0 ZrO₂ 2.9 2.9 P₂O₅ 1.3 1.3 Y₂O₃ 0 0 SnO₂ 0 0 Phaselithium disilicate lithium disilicate assemblage Ceramming 2 hr at 750°C., 2 hr at 750° C., cycle 4 hr at 850° C. 4 hr at 850° C. AppearanceGlassy, Glassy, translucent translucent Ceramming 2 hr at 750° C., 2 hrat 750° C., cycle 4 hr at 875° C. 4 hr at 875° C. Appearance Glassy,Glassy, translucent translucent Ceramming 2 hr at 750° C., 2 hr at 750°C., cycle 4 hr at 900° C. 4 hr at 900° C. Appearance Glassy, Glassy,translucent translucent Note: in Table 3 tetragonal ZrCh is denoted by“t-ZrCh,” monoclinic ZrO₂ is denoted by “m-ZrCh,” and quartz solidsolution is denoted by “quartz s.s.”

In some embodiments, the glass precursor and/or the glass ceramic can bestrengthened to include compressive stress (CS) that extends from asurface thereof to a depth of compression (DOC). The compressive stressregions are balanced by a central portion exhibiting a tensile stress.At the DOC, the stress crosses from a positive (compressive) stress to anegative (tensile) stress. In one or more embodiments, the glass articlemay be chemically strengthening by ion exchange or other methods knownin the art. In some embodiments, the residual glass phase or the glassprecursor to the glass ceramic comprises at least one of lithium sodiumor potassium, which enables ion exchange. Ion exchange is commonly usedto chemically strengthen glasses. In one particular example, alkalications within a source of such cations (e.g., a molten salt, or “ionexchange,” bath) are exchanged with smaller alkali cations within theglass to achieve a layer under a compressive stress (CS) extending fromthe surface of the glass to a depth of compression (DOC) within theglass phase. For example, potassium ions from the cation source areoften exchanged with sodium and/or lithium ions within the glass phase,and the K⁺ concentration profile correlates with the compressive stressand depth of layer.

The glass ceramic or precursor glass may be ion exchanged by immersionin at least one ion exchange bath containing molten salts (e.g.,nitrates, sulfides, halides, or the like) of at least one alkali metalsuch as lithium, sodium, or potassium. The ion exchange bath may containa salt (or salts) of a single alkali metal (e.g., sulfides, nitrates, orhalides of Li, Na, or K) or salts of two or more alkali metals (e.g.,sulfides, nitrates, or halides of Li and Na, or sulfides, nitrates, orhalides of Na and K). Ion exchange is carried out in the ion exchangebath at temperatures ranging from about 390° C. to about 550° C. fortimes ranging from about 0.5 hour to about 24 hours.

The precursor glass or glass ceramic, in some embodiments, is ionexchanged and has a compressive layer extending from a surface to adepth of compression (DOC) of at least about 10 μm or, in someembodiments, at least about 30 μm into the glass ceramic, or in someembodiments up to about 10, 15, 20 or 25% into the glass as measured bythickness (surface to center). In some embodiments, the compressivelayer extends from the surface of the precursor glass or glass ceramicto a depth of up to about 20% of the thickness of the glass ceramic. Insome embodiments, the precursor glass or glass ceramic may bestrengthened to exhibit a surface compressive stress in a range from 250MPa to 800 MPa or greater.

In the strengthened glass ceramic, the depth of the compressive layermay be determined by electron microprobe, glow-discharge opticalemission spectroscopy (GDOES, which is a technique for measuring depthprofiles of constituent elements in a solid sample by detectingemissions from atoms accommodated in plasma by sputtering), or similartechniques that can provide composition data as a function of depth,where data would show incorporation of Na (where Na⁺ replaces Li⁺ in theglass phase) and/or K at the surfaces. The DOC of a precursor glass maybe measured by surface stress meter (FSM) using commercially availableinstruments such as the FSM-6000, manufactured by Orihara IndustrialCo., Ltd. (Japan). Surface stress measurements rely upon the accuratemeasurement of the stress optical coefficient (SOC), which is related tothe birefringence of the glass. SOC in turn is measured by those methodsthat are known in the art, such as fiber and four point bend methods,both of which are described in ASTM standard C770-98 (2013), entitled“Standard Test Method for Measurement of Glass Stress-OpticalCoefficient,” the contents of which are incorporated herein by referencein their entirety, and a bulk cylinder method. CS may also be measuredby measured by FSM. As used herein CS may be the “maximum compressivestress” which is the highest compressive stress value measured withinthe compressive stress layer. In some embodiments, the maximumcompressive stress is located at the surface of the precursor glass orglass ceramic. In other embodiments, the maximum compressive stress mayoccur at a depth below the surface, giving the compressive profile theappearance of a “buried peak.”

The strengthened articles disclosed herein may be incorporated intoanother article such as an article with a display (or display articles)(e.g., consumer electronics, including mobile phones, tablets,computers, navigation systems, and the like), architectural articles,transportation articles (e.g., automotive, trains, aircraft, sea craft,etc.), appliance articles, or any article that would benefit from sometransparency, scratch-resistance, abrasion resistance or a combinationthereof. In other embodiments, the glass ceramic forms a portion of aconsumer electronic product, such as a cellular phone or smart phone,laptop computer, tablet, or the like. Such consumer electronic productstypically comprise a housing having front, back, and side surfaces, andinclude electrical components such as a power source, a controller, amemory, a display, and the like, which are at least partially internalto the housing. In some embodiments, the glass ceramic described hereincomprises at least a portion of a protective element, such as, but notlimited to, the housing and/or display of a consumer electronic product.

An exemplary article incorporating any of the strengthened articlesdisclosed herein is shown in FIGS. 5A and 5B. Specifically, FIGS. 5A and5B show a consumer electronic device 500 including a housing 502 havingfront 504, back 506, and side surfaces 508; electrical components (notshown) that are at least partially inside or entirely within the housingand including at least a controller, a memory, and a display 510 at oradjacent to the front surface of the housing; and a cover substrate 512at or over the front surface of the housing such that it is over thedisplay. In some embodiments, at least one of the cover substrate 512 ora portion of housing 502 may include any of the strengthened articlesdisclosed herein.

The ZrO₂-toughened glass-ceramic materials described herein can havefracture toughness values, as measured by Chevron notch short barmethods (known in the art and described in ASTM procedure E1304-97), ofat least 1 MPa·m^(1/2), 1.5 MPa·m^(1/2), 2 MPa·m^(1/2), 3 MPa·m^(1/2),or in some embodiments, at least 4 MPa·m^(1/2). In some embodiments, thefracture toughness is in a range from 1 MPa·m^(1/2), 1.5 MPa·m^(1/2), 2MPa·m^(1/2), 3 MPa·m^(1/2), or 4 MPa·m^(1/2) to 6 MPa·m^(1/2), 8MPa·m^(1/2), or 10 MPa·m^(1/2) and, in other embodiments, from about 1.5MPa·m^(1/2), 2 MPa·m^(1/2), 3 MPa·m^(1/2) to 8 MPa·m^(1/2). Results offracture toughness and flex strength measurements for selected samplesare provided in Table 3. Examples 5-12 in Table 3 illustrate theincrease in fracture toughness with increasing amounts of ZrO₂.

In some embodiments, the ZrO₂-toughened glass ceramic described hereinis used in dental composites, restorative materials, and articles suchas, but not limited to, fillings, bridges, splints, crowns, partialcrowns, dentures, teeth, jackets, inlays, onlays, facings, veneers,facets, implants, cylinders, abutments and connectors. In addition tothe glass ceramic, such dental composites, restorative materials, andarticles may also include further additives such as, but not limited to,stabilizers, flavorings, colorants (e.g., Mn, V, Ti, Fe, Er, Co, Pr, Tb,Cr, Nd, Ce, V, Eu, Ho, Ni, and Cu, oxides and sulfides thereof, andcombinations thereof), microbiocidal active ingredients, fluorideion-releasing additives, optical brighteners, plasticizers, UVabsorbers, and/or solvents such as water, ethanol, or correspondingsolvent mixtures. The glass ceramic may be processed into the dentalarticle using various methods including, but not limited to, injectionmolding, gel-casting, slip casting, or electroforming, hand forming,CAD/CAM methods, 3d printing, and other various rapid prototypingmethods that are known in the art. The glass ceramic may, in someembodiments, be ground to powder, which may be then formed into asuspension, pellet, feedstock material or a pre-sintered blank priorbeing formed into the dental article.

Processes for Making Glass Ceramics and Glass Ceramic Precursors

Precursor glasses having the oxide contents listed in Table 1 can bemade via traditional methods. For example, in some embodiments, theprecursor glasses can be formed by thoroughly mixing the requisite batchmaterials (for example, using a turbular mixer) in order to secure ahomogeneous melt, and subsequently placing into silica and/or platinumcrucibles. The crucibles can be placed into a furnace and the glassbatch melted and maintained at temperatures ranging from 1250-1650° C.for times ranging from about 6-16 hours. The melts can thereafter bepoured into steel molds to yield glass slabs. Subsequently, those slabscan be transferred immediately to an annealer operating at about500-650° C., where the glass is held at temperature for about 1 hour andsubsequently cooled overnight. In another non-limiting example,precursor glasses are prepared by dry blending the appropriate oxides,carbonates, and mineral sources for a time sufficient to thoroughly mixthe ingredients. The glasses are melted in platinum crucibles attemperatures ranging from about 1100° C. to about 1650° C. and held attemperature for about 16 hours. The resulting glass melts are thenpoured onto a steel table to cool. The precursor glasses are thenannealed at appropriate temperatures.

Once the glass compositions have been made, the resulting precursorglasses can be cerammed by heat treating. Heat treating is carried outunder conditions that lead to crystallization of the glass compositionto make a ceramic. Generally, this is done via a two-phase heatingprocess, wherein the glass is first heated to a lower temperature toinduce nucleation, and then heated to a higher temperature to inducecrystallization. Non-limiting conditions include first heating to 600°C. to 850° C., 635° C. to 800° C., or 650° C. to 750° C. for from 0.1 to10 hours, 0.25 to 8 hours, 0.25 to 5 hours, 0.25 to 3 hours, 0.25 to 2hours, 0.5 to 8 hours, 0.5 to 5 hours, 0.5 to 3 hours, 0.5 to 2 hours, 1to 9 hours, 1 to 8 hours, 1 to 5 hours, 1 to 3 hours, or 1 to 2 hours,(called a nucleation step), followed by heating at 725° C. to 1000° C.,725° C. to 950° C., 725° C. to 900° C., or 750° C. to 850° C. for 0.1 to8 hours 0.1 to 10 hours, 0.25 to 8 hours, 0.25 to 5 hours, 0.25 to 3hours, 0.25 to 2 hours, 0.5 to 8 hours, 0.5 to hours, 0.5 to 3 hours,0.5 to 2 hours, 1 to 9 hours, 1 to 8 hours, 1 to 5 hours, 1 to 3 hours,1 to 2 hours, 2 to 9 hours, 2 to 8 hours, 2 to 5 hours, 2 to 3 hours, or2 to 4 hours (a crystal growth step).

In an example embodiment, a precursor glass comprising at least about 18wt % Li₂O, up to about 5 wt % Al₂O₃, and at least about 4 wt % ZrO₂ isfirst provided. The precursor glass is next heat-treated or “cerammed”to form the glass ceramic. The ceramming step comprises first heatingthe precursor material at a first temperature in a range from about 600°C. to about 750° C. for a first time period ranging from about 15minutes to about 2.5 hours or, in some embodiments, from about 15minutes to about one hour or, in other embodiments, from about 1.5 hoursto about 2.5 hours. Following the first heating step, the material isheated at a second temperature in a range from about 725° C. to about1000° C. for a second time period ranging from about 0.5 hour to about 5hours, or, in some embodiments, from about 0.5 hour to about 5 hours or,in other embodiments, from about 3 hours to about 5 hours to form theglass ceramic.

Alternatively, in some embodiments, the precursor material may comprisea precursor glass and a ceramic powder, wherein the ceramic powdercomprises ZrO₂. In this embodiment, the precursor glass may be ground toa powder having an average grain size of less than about 10 μm and thenmixed with the ceramic powder. The glass ceramic may then, in someembodiments, be sintered at temperatures ranging from about 650° C. toabout 800° C. for a time ranging from about 0.5 hour up to about 4hours. In other embodiments, the glass ceramic may be hot pressed toform a near-net shape.

While in some embodiments ZrO₂-toughened glass-ceramics have been madeby adding ZrO₂ particles to a powdered glass-ceramic precursor glass,with subsequent sintering, such methods involve mixing of two dissimilarpowders, which can lead inhomogeneity in the final ZrO₂-glass-ceramicproduct. In addition, the sintering times and temperatures that are usedmay promote more grain growth than desired or may have other detrimentaleffects on microstructure. In the sintering method, nucleation andgrowth of the desired phases may be a mixture of surface and bulknucleation, thereby resulting in microstructures that are difficult tocontrol or repeat. All of these challenges could result in compromisedstrength and/or fracture toughness values of the final material.Furthermore, sintering is often done at elevated pressures in an attemptto reach full density of the final product. Achieving full density mayor may not be achieved and porosity may be an issue for realizing highstrength and fracture toughness materials.

Producing ZrO₂-containing glass ceramics from homogeneous glassprecursors, as described herein, addresses many of the above issues. Theglasses may be homogeneously nucleated and the nucleation and growthsteps can be further controlled to yield final products with optimizedmicrostructures and phase assemblages. Full density is achieved throughthe ceramming of the dense precursor glass without the use of elevatedpressure. Precursor glasses are produced by conventional glass meltingand forming techniques. Whereas some glass compositions containing highamounts of ZrO₂ must be melted at high temperature, many of the Li₂O andMgO-containing compositions described herein are easily melted at lowtemperatures (e.g., <1650° C.). Further, additional phases, previouslydescribed hereinabove such as lithium metasilicate, lithium disilicate,b-quartz solid solution, b-spodumene solid solution, may also beprecipitated in the glass ceramic. In some embodiments, thesemicrostructures and phase assemblages are not easily obtainable usingceramic processing routes.

Another advantage of the materials described herein is that they havethe ability to be partially cerammed to the lithium metasilicate phase,then machined and/or finished, and then cerammed into the full highfracture toughness final glass ceramic. When ceramming, lithiummetasilicate comes out first (leaving a ZrO₂-rich glass phase), allowingfor shaping or machining, then further ceramming to get t-ZrO₂/LDSphases. In some embodiments, the ZrO₂-toughened glass ceramic describedherein is used in applications such as, but not limited to valves,blades, cutting tools, knives, components for semiconductormanufacturing (cover rings, etch nozzles, RF shields, etc.), oil and gasdrilling components (downhole pump plungers, control valves, etc.), andferrules for optical fiber connectors, where high resistance tomechanical wear is desired.

The glass ceramics and precursor glasses described herein are easilycast or rolled as homogeneous glasses, and final geometries such assheets or boules are obtainable. The resultant glass ceramic can beprovided as a sheet, which can then be reformed by pressing, blowing,bending, sagging, vacuum forming, or other means into curved or bentpieces of uniform thickness. Reforming can be done before thermallytreating or the forming step can also serve as a thermal treatment stepwhere both forming and thermally treating are performed substantiallysimultaneously.

Examples

FIGS. 1A and 1B are scanning electron microscopy (SEM) images showingembodied glass ceramics having ZrO₂ and other phases present in samples.FIG. 1A is an image of a glass ceramic material (composition Example 6in Table 3) that is cerammed by first heating at 750° C. for 2 hours andthen heating at 900° C. for 4 hours, and FIG. 1B is an image of a glassceramic material (composition Example 10 in Table 3) that is cerammed byfirst heating at 800° C. for 2 hours and then heating at 900° C. for 4hours. The microstructure of the materials in both images ishomogeneous. The dark gray rods 120 in FIGS. 1A and 1B are lithiumdisilicate and the white phases 110 in FIGS. 1A and 1B are ZrO₂. TheZrO₂ grains 110 are on the order of about 1 μm in size. X-Raydiffraction studies of these samples reveals that the zirconia phase isprimarily tetragonal ZrO₂. The sample that is cerammed at 900° C. (FIG.1B) appears by SEM to contain a higher amount of the tetragonal ZrO₂phase than the sample cerammed at 800° C. for 4 hours (FIG. 1A).

FIGS. 2A-D are SEM images of an indented area on the surface of a glassceramic (composition Example 6 in Table 3) that is cerammed by firstheating at 750° C. for 2 hours and then heating at 875° C. for 4 hours,showing a crack at different magnifications (FIG. 2A at 100×magnification; FIG. 2B at 500×; FIG. 2C at 2500×; FIG. 2D at 10,000×).Under indentation load of 50 kgf, the sample exhibits crack deflectionand tortuous crack path which are indicative of toughening mechanisms.

FIGS. 3A-D show the crystal microstructure of an embodiment (Example 8)along with SEM elemental mapping of some of the constituents of Example8, where FIG. 3B shows the silicon present in the material, FIG. 3Cshows the zirconia, and FIG. 3D shows the phosphorous

FIGS. 4A-4D are X-ray diffraction spectra showing phase assemblages ofembodied glass-ceramics. The figures show that lithium disilicate (LS2)and tetragonal ZrO₂ (t-ZrO₂) are present in the various embodimentsalong with a number of other phases (lithium metasilicate (LMS),monoclinic ZrO₂ (m-ZrO₂)). FIG. 4A shows the phase assemblage forExample 8, FIG. 4B for Example 14, FIG. 4C for Example 40, and FIG. 4Dfor Example 44. All examples were cerammed at 750° C. for 2 hours, then875° C. for 4 hours, except Example 44 which was cerammed at 750° C. for2 hours, then 850° C. for 4 hours.

FIG. 5 is a plot of abraded ring-on-ring (ARoR) data obtained for 0.8mm-thick samples of a non-ion exchanged and ion-exchanged ZrO₂-toughenedglass ceramic (Example 8), which ion exchanged for a number of differenttimes and temperatures. The glass ceramic was cerammed by first heatingat 700° C. for 2 hours and then heating at 850° C. for 4 hours. Thering-on-ring test is a flexural strength measurement known in the artfor testing flat glass and glass ceramic specimens and is described inASTM C1499-09(2013), entitled “Standard Test Method for MonotonicEquibiaxial Flexural Strength of Advanced Ceramics at AmbientTemperature.” ASTM C1499-09(2013) serves as the basis for thering-on-ring test methodology described herein. In some instances, theglass ceramic samples are abraded prior to ring-on-ring testing with 15grit silicon carbide (SiC) particles that are delivered to the glasssample using the method and apparatus described in Annex A2, entitled“Abrasion Procedures,” of ASTM C158-02(2012), entitled “Standard TestMethods for Strength of Glass by Flexure (Determination of Modulus ofRupture). The contents of ASTM C1499-09(2013) and ASTM C158-02(2012),Annex 2, are incorporated herein by reference in their entirety. Thetable shows that the glass ceramics embodied herein are capable ofundergoing ion exchange and that such ion-exchanged glass ceramics haveimproved load to failure values that correlate with time and temperaturein the ion exchange bath.

FIGS. 6A and 6B are comparisons of drop performance for exampleembodiments (Example 14) and ZrO₂ ceramics. All parts are 0.8 mm thick,dropped on 180 grit sandpaper and then survivors on 30 grit sandpaper.Example 14 was cerammed at 750° C. for 2 hours, then 875° C. for 4hours; Comp 1 is a reference transparent glass-ceramic; CoorsTek TTZ isa MgO-stablized ZrO₂ ceramic. The embodied compositions have favorableproperties when compared to the transparent glass ceramic and in linewith the CoorsTek material. Similarly, FIGS. 9A-9C are micrographs ofscratch tests done using a Knoop tip at 14 N and 16 N loads for Example8. The example composition was cerammed at 750° C. for 2 hours, then875° C. for 4 hours.

The color of Example 8 is measured in CIELAB color space coordinates(determined from reflectance spectra measurements using aspectrophotometer, with illuminant D65 and specular reflectanceexcluded), a*: −0.15, b*: −0.31, and L*: 98.8. FIG. 7 shows the losstangent of Example 8 versus a reference glass and reference glassceramic. The example composition was cerammed at 750° C. for 2 hours,then 875° C. for 4 hours. FIG. 8 shows the dielectric constant ofExample 8 versus a reference glass and reference glass ceramic. Theexample composition was cerammed at 750° C. for 2 hours, then 875° C.for 4 hours.

While typical embodiments have been set forth for the purpose ofillustration, the foregoing description should not be deemed to be alimitation on the scope of the disclosure or appended claims.Accordingly, various modifications, adaptations, and alternatives mayoccur to one skilled in the art without departing from the spirit andscope of the present disclosure or appended claims.

The invention claimed is:
 1. A glass ceramic comprising: a firstcrystalline phase comprising: a tetragonal ZrO₂ phase; a secondcrystalline phase comprising a lithium silicate; and a residual glassphase; wherein the glass ceramic comprises a fracture toughness of from1 to 10 MPa·m^(1/2), as measured by Chevron notch short bar methods; andwherein the tetragonal ZrO₂ comprises a weight percent (wt %) of thetotal ZrO₂ in the glass ceramic, measured as the (((weight of thetetragonal ZrO₂)/(total weight of ZrO₂ in the glass ceramic))*100), andwherein the tetragonal ZrO₂ comprises 40-95 wt % of ZrO₂ in the glassceramic.
 2. The glass ceramic of claim 1, comprising the composition:50-80 mol % SiO₂, 18-40 mol % Li₂O, 1.5-25 mol % ZrO₂, and greater than0-5 mol % P₂O₅.
 3. The glass ceramic of claim 1, wherein the at leasttwo crystalline phases comprise a weight percent (wt %) of the totalglass ceramic, measured as the (((weight of the at least two crystallinephases)/(total weight of the glass ceramic))*100), and wherein the atleast two crystalline phases comprise from 60-95 wt % of the total glassceramic.
 4. The glass ceramic of claim 1, wherein the tetragonal ZrO₂crystals have an average crystal size from 0.1 to 10 μm along theirlongest dimension.
 5. The glass ceramic of claim 1, wherein the lithiumsilicate comprises a weight percent (wt %) of the total glass ceramic,measured as the (((weight of the lithium silicate)/(total weight theglass ceramic))*100), and wherein the lithium silicate comprises from25-60 wt % of the total glass ceramic composition.
 6. The glass ceramicof claim 1, wherein the lithium silicate crystals have an averagecrystal size from 1 to 20 μm along their longest dimension.
 7. The glassceramic of claim 1, further comprising one or more additionalcrystalline phases, wherein the one or more additional crystallinephases is selected from the group consisting of lithium aluminosilicate,cristobalite, β-spodumene, lithiophosphate, lithium orthophosphate,β-quartz solid solution, α-quartz, baddeleyite, lithium metasilicate,cristobalite, monoclinic zirconia, cubic zirconia, zekzerite,(Na,Li)ZrSi₆O₁₈ and combinations thereof.
 8. The glass ceramic of claim7, wherein the one or more additional crystalline phases is two or morephases one of which is monoclinic ZrO₂ and the second is selected fromthe group consisting of lithium aluminosilicate, β-spodumene solidsolution, β-quartz solid solution, or α-quartz, wherein the monoclinicZrO₂ is from >0-5 wt % of the glass ceramic.
 9. The glass ceramic ofclaim 1, further comprising: 0-5 mol % Al₂O₃ and 0-5 mol % Na₂O.
 10. Theglass ceramic of claim 1, further comprising: 0-14 mol % R₂O, whereinR₂O is the sum of the alkali metal oxides Na₂O, K₂O, and Cs₂O, 0-10 mol% MO, wherein MO is the sum of the alkaline earth metal oxides MgO, CaO,SrO, and BaO, >0-5 mol % TMO, wherein TMO is the sum of oxides of metalsin groups IVB-VIII, IB, and IIB, or 4-12 in the periodic table, and 0-5mol % REO, wherein REO is the sum of oxides Sc₂O₃, Y₂O₃, and thelanthanides La₂O₃, Ce₂O₃, Pr₂O₃, Nd₂O₃, Pm₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃,Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃.
 11. The glassceramic of claim 1, comprising: 55-70 mol % SiO₂ 18-30 mol % Li₂O 4-20mol % ZrO₂, and 0.2-5 mol % P₂O₅.
 12. The glass ceramic of claim 1,comprising: 58-69 mol % SiO₂ 25-36 mol % Li₂O 6-15 mol % ZrO₂ >0-5 mol %Al₂O₃ 0-5 mol % Na₂O 0-5 mol % B₂O₃ 0.2-3 mol % P₂O₅ 0-8 mol % MO,wherein MO is the sum of the alkaline earth metal oxides MgO, CaO, SrO,and BaO, >0-5 mol % TMO, wherein TMO is the sum of oxides of metals ingroups IVB-VIII, IB, and IIB, or 4-12 in the periodic table, and 0-5 mol% REO, wherein REO is the sum of oxides Sc₂O₃, Y₂O₃, and the lanthanidesLa₂O₃, Ce₂O₃, Pr₂O₃, Nd₂O₃, Pm₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃,Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃.
 13. The glass ceramic of claim 1,further comprising >0-5 mol % REO wherein REO is oxides of scandium,yttrium, and the lanthanides.
 14. The glass ceramic of claim 1, whereinthe glass ceramic is free of Rb₂O and Cs₂O.
 15. The glass ceramic ofclaim 1, wherein the glass ceramic further comprises >0-5 mol % TiO₂.16. The glass ceramic of claim 1, further comprising >0-3 mol % ZnO. 17.The glass ceramic of claim 1, further comprising >0-4 mol % of a colorcomponent comprising a metal oxide.
 18. The glass ceramic of claim 1,wherein the glass ceramic exhibits a color presented in CIELAB colorspace coordinates: a*=from about −1 to about +3; b*=from about −7 toabout +3; and L*>85; or a*=from about −1 to about 1; b*=from about −4 toabout 1; and L*<60.
 19. The glass ceramic of claim 1, wherein the glassceramic comprises an ion exchanged layer having a depth of compressionof at least 10 μm.
 20. A glass ceramic comprising: a first crystallinephase comprising: a tetragonal ZrO₂ phase; a second crystalline phasecomprising a lithium silicate; and a residual glass phase; wherein theglass ceramic comprises a fracture toughness of from 1 to 10MPa.m^(1/2), as measured by Chevron notch short bar methods; and whereinthe glass ceramic comprises: 58-69 mol% SiO₂ 25-36 mol% Li₂O 6-15 mol%ZrO₂ >0-5 mol% Al₂O₃ 0-5 mol% Na₂O 0-5 mol% B₂O₃ 0.2-3 mol% P₂O₅ 0-8mol% MO, wherein MO is the sum of the alkaline earth metal oxides MgO,CaO, SrO, and BaO, >0-5 mol% TMO, wherein TMO is the sum of oxides ofmetals in groups IVB-VIII, IB, and IIB, or 4-12 in the periodic table,and 0-5 mol% REO, wherein REO is the sum of oxides Sc₂O₃, Y₂O₃, and thelanthanides La₂O₃, Ce₂O₃, Pr₂O₃, Nd₂O₃, Pm₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃,Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃.
 21. The glassceramic of claim 20, wherein the at least two crystalline phasescomprise a weight percent (wt%) of the total glass ceramic, measured asthe (((weight of the at least two crystalline phases)/(total weight ofthe glass ceramic))*100), and wherein the at least two crystallinephases comprise from 60-95 wt% of the total glass ceramic.
 22. The glassceramic of claim 20, wherein: the tetragonal ZrO₂ crystals have anaverage crystal size from 0.1 to 10 μm along their longest dimension;and/or the lithium silicate crystals have an average crystal size from 1to 20 μm along their longest dimension.
 23. The glass ceramic of claim20, wherein the lithium silicate comprises a weight percent (wt%) of thetotal glass ceramic, measured as the (((weight of the lithiumsilicate)/(total weight the glass ceramic))*100), and wherein thelithium silicate comprises from 25-60 wt% of the total glass ceramiccomposition.
 24. The glass ceramic of claim 20, wherein the glassceramic exhibits a color presented in CIELAB color space coordinates:a*=from about −1 to about +3; b*=from about −7 to about +3; and L*>85;or a*=from about −1 to about 1; b*=from about −4 to about 1; and L*<60.